{"id":470,"date":"2023-05-28T01:48:48","date_gmt":"2023-05-27T17:48:48","guid":{"rendered":"https:\/\/xinchewhd.com.cn\/?p=470"},"modified":"2023-05-28T01:48:50","modified_gmt":"2023-05-27T17:48:50","slug":"1-8w-%e5%ad%97%e7%9a%84-sql-%e4%bc%98%e5%8c%96%e5%a4%a7%e5%85%a8","status":"publish","type":"post","link":"https:\/\/xinchewhd.com.cn\/index.php\/mysql\/1-8w-%e5%ad%97%e7%9a%84-sql-%e4%bc%98%e5%8c%96%e5%a4%a7%e5%85%a8\/","title":{"rendered":"1.8w \u5b57\u7684 SQL \u4f18\u5316\u5927\u5168"},"content":{"rendered":"<div class=\"wxsyncmain\">\n<p style=\"text-align: center;\" data-mpa-powered-by=\"yiban.io\"><span style=\"color: #ffa900; font-size: 15px;\">\u2193<\/span><span style=\"color: #ffa900; font-size: 15px;\">\u63a8\u8350\u5173\u6ce8\u2193<\/span><\/p>\n<section class=\"mp_profile_iframe_wrp\"><\/section>\n<section style=\"font-size: 16px; color: black; padding-right: 10px; padding-left: 10px; line-height: 1.6; letter-spacing: 0px; word-break: break-word; text-align: left; font-family: Helvetica;\" data-tool=\"mdnice\u7f16\u8f91\u5668\" data-website=\"https:\/\/www.mdnice.com\">\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5206\u4eab\u4e00\u7bc7\u5173\u4e8eSQL\u4f18\u5316\u7684\u786c\u6838\u6587\u7ae0\uff0c\u5168\u6587\u6709\u70b9\u957f\uff0c\u5efa\u8bae\u6536\u85cf\u540e\u6162\u6162\u770b\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f88\u591a\u670b\u53cb\u5728\u505a\u6570\u636e\u5206\u6790\u65f6\uff0c\u5206\u6790\u4e24\u5206\u949f\uff0c\u8dd1\u6570\u4e24\u5c0f\u65f6\uff1f<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5728\u4f7f\u7528SQL\u8fc7\u7a0b\u4e2d\u4e0d\u4ec5\u8981\u5173\u6ce8\u6570\u636e\u7ed3\u679c\uff0c\u540c\u6837\u8981\u6ce8\u610fSQL\u8bed\u53e5\u7684\u6267\u884c\u6548\u7387\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u672c\u6587\u6d89\u53ca\u4e09\u90e8\u5206\uff1a<\/p>\n<ul class=\"list-paddingleft-1\" style=\"margin-top: 8px; margin-bottom: 8px; padding-left: 25px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">SQL\u4ecb\u7ecd<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">SQL\u4f18\u5316\u65b9\u6cd5<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">SQL\u4f18\u5316\u5b9e\u4f8b<\/section>\n<\/li>\n<\/ul>\n<h1 style=\"margin-bottom: 15px; font-weight: bold; font-size: 24px; margin-top: 16px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><span style=\"font-size: 18px;\">1\u3001MySQL\u7684\u57fa\u672c\u67b6\u6784<\/span><\/h1>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09MySQL\u7684\u57fa\u7840\u67b6\u6784\u56fe<\/strong><\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005451301.jpeg\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5642076502732241\" data-type=\"jpeg\" data-w=\"732\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005451301.jpeg\" data-ratio=\"0.5642076502732241\" data-type=\"jpeg\" data-w=\"732\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5de6\u8fb9\u7684client\u53ef\u4ee5\u770b\u6210\u662f\u5ba2\u6237\u7aef\uff0c\u5ba2\u6237\u7aef\u6709\u5f88\u591a\uff0c\u50cf\u6211\u4eec\u7ecf\u5e38\u4f60\u4f7f\u7528\u7684CMD\u9ed1\u7a97\u53e3\uff0c\u50cf\u6211\u4eec\u7ecf\u5e38\u7528\u4e8e\u5b66\u4e60\u7684WorkBench\uff0c\u50cf\u4f01\u4e1a\u7ecf\u5e38\u4f7f\u7528\u7684Navicat\u5de5\u5177\uff0c\u5b83\u4eec\u90fd\u662f\u4e00\u4e2a\u5ba2\u6237\u7aef\u3002\u53f3\u8fb9\u7684\u8fd9\u4e00\u5927\u5806\u90fd\u53ef\u4ee5\u770b\u6210\u662fServer(MySQL\u7684\u670d\u52a1\u7aef)\uff0c\u6211\u4eec\u5c06Server\u5728\u7ec6\u5206\u4e3asql\u5c42\u548c\u5b58\u50a8\u5f15\u64ce\u5c42\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u67e5\u8be2\u51fa\u6570\u636e\u4ee5\u540e\uff0c\u4f1a\u8fd4\u56de\u7ed9\u6267\u884c\u5668\u3002\u6267\u884c\u5668\u4e00\u65b9\u9762\u5c06\u7ed3\u679c\u5199\u5230\u67e5\u8be2\u7f13\u5b58\u91cc\u9762\uff0c\u5f53\u4f60\u4e0b\u6b21\u518d\u6b21\u67e5\u8be2\u7684\u65f6\u5019\uff0c\u5c31\u53ef\u4ee5\u76f4\u63a5\u4ece\u67e5\u8be2\u7f13\u5b58\u4e2d\u83b7\u53d6\u5230\u6570\u636e\u4e86\u3002\u53e6\u4e00\u65b9\u9762\uff0c\u76f4\u63a5\u5c06\u7ed3\u679c\u54cd\u5e94\u56de\u5ba2\u6237\u7aef\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09\u67e5\u8be2\u6570\u636e\u5e93\u7684\u5f15\u64ce<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 show engines;<\/strong><\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005452700.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.4746317512274959\" data-type=\"png\" data-w=\"611\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005452700.png\" data-ratio=\"0.4746317512274959\" data-type=\"png\" data-w=\"611\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 show variables like \u201c%storage_engine%\u201d;<\/strong><\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005452342.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.4691689008042895\" data-type=\"png\" data-w=\"373\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005452342.png\" data-ratio=\"0.4691689008042895\" data-type=\"png\" data-w=\"373\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\uff09\u6307\u5b9a\u6570\u636e\u5e93\u5bf9\u8c61\u7684\u5b58\u50a8\u5f15\u64ce<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">create\u00a0table\u00a0tb(\n\u00a0\u00a0\u00a0\u00a0id\u00a0int(4)\u00a0auto_increment,\n\u00a0\u00a0\u00a0\u00a0name\u00a0varchar(5),\n\u00a0\u00a0\u00a0\u00a0dept\u00a0varchar(5),\n\u00a0\u00a0\u00a0\u00a0primary\u00a0key(id)\n)\u00a0engine=myISAM\u00a0auto_increment=1\u00a0default\u00a0charset=utf8;\n<\/code><\/pre>\n<h1 style=\"margin-bottom: 15px; font-weight: bold; font-size: 24px; margin-top: 16px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><span style=\"font-size: 18px;\">SQL\u4f18\u5316<\/span><\/h1>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09\u4e3a\u4ec0\u4e48\u9700\u8981\u8fdb\u884cSQL\u4f18\u5316\uff1f<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5728\u8fdb\u884c\u591a\u8868\u8fde\u63a5\u67e5\u8be2\u3001\u5b50\u67e5\u8be2\u7b49\u64cd\u4f5c\u7684\u65f6\u5019\uff0c\u7531\u4e8e\u4f60\u5199\u51fa\u7684SQL\u8bed\u53e5\u6b20\u4f73\uff0c\u5bfc\u81f4\u7684\u670d\u52a1\u5668\u6267\u884c\u65f6\u95f4\u592a\u957f\uff0c\u6211\u4eec\u7b49\u5f85\u7ed3\u679c\u7684\u65f6\u95f4\u592a\u957f\u3002\u57fa\u4e8e\u6b64\uff0c\u6211\u4eec\u9700\u8981\u5b66\u4e60\u600e\u4e48\u4f18\u5316SQL\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09mysql\u7684\u7f16\u5199\u8fc7\u7a0b\u548c\u89e3\u6790\u8fc7\u7a0b<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u7f16\u5199\u8fc7\u7a0b<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">select\u00a0dinstinct\u00a0\u00a0..from\u00a0\u00a0..join\u00a0..on\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0..group\u00a0by\u00a0..having\u00a0..order\u00a0by\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">limit<\/span>\u00a0..\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u89e3\u6790\u8fc7\u7a0b<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">from\u00a0..\u00a0on..\u00a0join\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0..group\u00a0by\u00a0..having\u00a0..select\u00a0dinstinct\u00a0..order\u00a0by\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">limit<\/span>\u00a0..\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u63d0\u4f9b\u4e00\u4e2a\u7f51\u7ad9\uff0c\u8be6\u7ec6\u8bf4\u660e\u4e86mysql\u89e3\u6790\u8fc7\u7a0b\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">https:\/\/www.cnblogs.com\/annsshadow\/p\/5037667.html<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\uff09SQL\u4f18\u5316\u2014\u4e3b\u8981\u5c31\u662f\u4f18\u5316\u7d22\u5f15<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4f18\u5316SQL\uff0c\u6700\u91cd\u8981\u7684\u5c31\u662f\u4f18\u5316SQL\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7d22\u5f15\u76f8\u5f53\u4e8e\u5b57\u5178\u7684\u76ee\u5f55\u3002\u5229\u7528\u5b57\u5178\u76ee\u5f55\u67e5\u627e\u6c49\u5b57\u7684\u8fc7\u7a0b\uff0c\u5c31\u76f8\u5f53\u4e8e\u5229\u7528SQL\u7d22\u5f15\u67e5\u627e\u67d0\u6761\u8bb0\u5f55\u7684\u8fc7\u7a0b\u3002\u6709\u4e86\u7d22\u5f15\uff0c\u5c31\u53ef\u4ee5\u5f88\u65b9\u4fbf\u5feb\u6377\u7684\u5b9a\u4f4d\u67d0\u6761\u8bb0\u5f55\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u4ec0\u4e48\u662f\u7d22\u5f15\uff1f<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7d22\u5f15\u5c31\u662f\u5e2e\u52a9MySQL\u9ad8\u6548\u83b7\u53d6\u6570\u636e\u7684\u4e00\u79cd\u3010\u6570\u636e\u7ed3\u6784\u3011\u3002\u7d22\u5f15\u662f\u4e00\u79cd\u6811\u7ed3\u6784\uff0cMySQL\u4e2d\u4e00\u822c\u7528\u7684\u662f\u3010B+\u6811\u3011\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u7d22\u5f15\u56fe\u793a\u8bf4\u660e(\u8fd9\u91cc\u7528\u4e8c\u53c9\u6811\u6765\u5e2e\u52a9\u6211\u4eec\u7406\u89e3\u7d22\u5f15)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6811\u5f62\u7ed3\u6784\u7684\u7279\u70b9\u662f\uff1a\u5b50\u5143\u7d20\u6bd4\u7236\u5143\u7d20\u5c0f\u7684\uff0c\u653e\u5728\u5de6\u4fa7\uff1b\u5b50\u5143\u7d20\u6bd4\u7236\u5143\u7d20\u5927\u7684\uff0c\u653e\u5728\u53f3\u4fa7\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8fd9\u4e2a\u56fe\u793a\u53ea\u662f\u4e3a\u4e86\u5e2e\u6211\u4eec\u7b80\u5355\u7406\u89e3\u7d22\u5f15\u7684\uff0c\u771f\u5b9e\u7684\u5173\u4e8e\u3010B+\u6811\u3011\u7684\u8bf4\u660e\uff0c\u6211\u4eec\u4f1a\u5728\u4e0b\u9762\u8fdb\u884c\u8bf4\u660e\u3002<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005453546.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.39814814814814814\" data-type=\"png\" data-w=\"1080\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005453546.png\" data-ratio=\"0.39814814814814814\" data-type=\"png\" data-w=\"1080\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7d22\u5f15\u662f\u600e\u4e48\u67e5\u627e\u6570\u636e\u7684\u5462\uff1f\u4e24\u4e2a\u5b57\u3010\u6307\u5411\u3011\uff0c\u4e0a\u56fe\u4e2d\u6211\u4eec\u7ed9age\u5217\u6307\u5b9a\u4e86\u4e00\u4e2a\u7d22\u5f15\uff0c\u5373\u7c7b\u4f3c\u4e8e\u53f3\u4fa7\u7684\u8fd9\u79cd\u6811\u5f62\u7ed3\u6784\u3002mysql\u8868\u4e2d\u7684\u6bcf\u4e00\u884c\u8bb0\u5f55\u90fd\u6709\u4e00\u4e2a\u786c\u4ef6\u5730\u5740\uff0c\u4f8b\u5982\u7d22\u5f15\u4e2d\u7684age=50\uff0c\u6307\u5411\u7684\u5c31\u662f\u6e90\u8868\u4e2d\u8be5\u884c\u7684\u6807\u8bc6\u7b26(\u201c\u786c\u4ef6\u5730\u5740\u201d)\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e5f\u5c31\u662f\u8bf4\uff0c\u6811\u5f62\u7d22\u5f15\u5efa\u7acb\u4e86\u4e0e\u6e90\u8868\u4e2d\u6bcf\u884c\u8bb0\u5f55\u786c\u4ef6\u5730\u5740\u7684\u6620\u5c04\u5173\u7cfb\uff0c\u5f53\u4f60\u6307\u5b9a\u4e86\u67d0\u4e2a\u7d22\u5f15\uff0c\u8fd9\u79cd\u6620\u5c04\u5173\u7cfb\u4e5f\u5c31\u5efa\u6210\u4e86\uff0c\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u7d22\u5f15\u5feb\u901f\u5b9a\u4f4d\u6e90\u8868\u4e2d\u8bb0\u5f55\u7684\u539f\u56e0\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4ee5\u3010select * from student where age=33\u3011\u67e5\u8be2\u8bed\u53e5\u4e3a\u4f8b\u3002\u5f53\u6211\u4eec\u4e0d\u52a0\u7d22\u5f15\u7684\u65f6\u5019\uff0c\u4f1a\u4ece\u4e0a\u5230\u4e0b\u626b\u63cf\u6e90\u8868\uff0c\u5f53\u626b\u63cf\u5230\u7b2c5\u884c\u7684\u65f6\u5019\uff0c\u627e\u5230\u4e86\u6211\u4eec\u60f3\u8981\u627e\u5230\u4e86\u5143\u7d20\uff0c\u4e00\u5171\u662f\u67e5\u8be2\u4e865\u6b21\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u6dfb\u52a0\u4e86\u7d22\u5f15\u4ee5\u540e\uff0c\u5c31\u76f4\u63a5\u5728\u6811\u5f62\u7ed3\u6784\u4e2d\u8fdb\u884c\u67e5\u627e\uff0c33\u6bd450\u5c0f\uff0c\u5c31\u4ece\u5de6\u4fa7\u67e5\u8be2\u5230\u4e8623\uff0c33\u5927\u4e8e23\uff0c\u5c31\u53c8\u67e5\u8be2\u5230\u4e86\u53f3\u4fa7\uff0c\u8fd9\u4e0b\u627e\u5230\u4e8633\uff0c\u6574\u4e2a\u7d22\u5f15\u7ed3\u675f\uff0c\u4e00\u5171\u8fdb\u884c\u4e863\u6b21\u67e5\u627e\u3002\u662f\u4e0d\u662f\u5f88\u65b9\u4fbf\uff0c\u5047\u5982\u6211\u4eec\u6b64\u65f6\u9700\u8981\u67e5\u627eage=62\uff0c\u4f60\u518d\u60f3\u60f3\u201c\u6dfb\u52a0\u7d22\u5f15\u201d\u524d\u540e\uff0c\u67e5\u627e\u6b21\u6570\u7684\u53d8\u5316\u60c5\u51b5\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>4\uff09\u7d22\u5f15\u7684\u5f0a\u7aef<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">1.\u5f53\u6570\u636e\u91cf\u5f88\u5927\u7684\u65f6\u5019\uff0c\u7d22\u5f15\u4e5f\u4f1a\u5f88\u5927(\u5f53\u7136\u76f8\u6bd4\u4e8e\u6e90\u8868\u6765\u8bf4\uff0c\u8fd8\u662f\u76f8\u5f53\u5c0f\u7684)\uff0c\u4e5f\u9700\u8981\u5b58\u653e\u5728\u5185\u5b58\/\u786c\u76d8\u4e2d(\u901a\u5e38\u5b58\u653e\u5728\u786c\u76d8\u4e2d)\uff0c\u5360\u636e\u4e00\u5b9a\u7684\u5185\u5b58\u7a7a\u95f4\/\u7269\u7406\u7a7a\u95f4\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">2.\u7d22\u5f15\u5e76\u4e0d\u9002\u7528\u4e8e\u6240\u6709\u60c5\u51b5\uff1aa.\u5c11\u91cf\u6570\u636e\uff1bb.\u9891\u7e41\u8fdb\u884c\u6539\u52a8\u7684\u5b57\u6bb5\uff0c\u4e0d\u9002\u5408\u505a\u7d22\u5f15\uff1bc.\u5f88\u5c11\u4f7f\u7528\u7684\u5b57\u6bb5\uff0c\u4e0d\u9700\u8981\u52a0\u7d22\u5f15\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">3.\u7d22\u5f15\u4f1a\u63d0\u9ad8\u6570\u636e\u67e5\u8be2\u6548\u7387\uff0c\u4f46\u662f\u4f1a\u964d\u4f4e\u201c\u589e\u3001\u5220\u3001\u6539\u201d\u7684\u6548\u7387\u3002\u5f53\u4e0d\u4f7f\u7528\u7d22\u5f15\u7684\u65f6\u5019\uff0c\u6211\u4eec\u8fdb\u884c\u6570\u636e\u7684\u589e\u5220\u6539\uff0c\u53ea\u9700\u8981\u64cd\u4f5c\u6e90\u8868\u5373\u53ef\uff0c\u4f46\u662f\u5f53\u6211\u4eec\u6dfb\u52a0\u7d22\u5f15\u540e\uff0c\u4e0d\u4ec5\u9700\u8981\u4fee\u6539\u6e90\u8868\uff0c\u4e5f\u9700\u8981\u518d\u6b21\u4fee\u6539\u7d22\u5f15\uff0c\u5f88\u9ebb\u70e6\u3002\u5c3d\u7ba1\u662f\u8fd9\u6837\uff0c\u6dfb\u52a0\u7d22\u5f15\u8fd8\u662f\u5f88\u5212\u7b97\u7684\uff0c\u56e0\u4e3a\u6211\u4eec\u5927\u591a\u6570\u4f7f\u7528\u7684\u5c31\u662f\u67e5\u8be2\uff0c\u201c\u67e5\u8be2\u201d\u5bf9\u4e8e\u7a0b\u5e8f\u7684\u6027\u80fd\u5f71\u54cd\u662f\u5f88\u5927\u7684\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>5\uff09\u7d22\u5f15\u7684\u4f18\u52bf<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">1.\u63d0\u9ad8\u67e5\u8be2\u6548\u7387(\u964d\u4f4e\u4e86IO\u4f7f\u7528\u7387)\u3002\u5f53\u521b\u5efa\u4e86\u7d22\u5f15\u540e\uff0c\u67e5\u8be2\u6b21\u6570\u51cf\u5c11\u4e86\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">2.\u964d\u4f4eCPU\u4f7f\u7528\u7387\u3002\u6bd4\u5982\u8bf4\u3010\u2026order by age desc\u3011\u8fd9\u6837\u4e00\u4e2a\u64cd\u4f5c\uff0c\u5f53\u4e0d\u52a0\u7d22\u5f15\uff0c\u4f1a\u628a\u6e90\u8868\u52a0\u8f7d\u5230\u5185\u5b58\u4e2d\u505a\u4e00\u4e2a\u6392\u5e8f\u64cd\u4f5c\uff0c\u6781\u5927\u7684\u6d88\u8017\u4e86\u8d44\u6e90\u3002\u4f46\u662f\u4f7f\u7528\u4e86\u7d22\u5f15\u4ee5\u540e\uff0c\u7b2c\u4e00\u7d22\u5f15\u672c\u8eab\u5c31\u5c0f\u4e00\u4e9b\uff0c\u7b2c\u4e8c\u7d22\u5f15\u672c\u8eab\u5c31\u662f\u6392\u597d\u5e8f\u7684\uff0c\u5de6\u8fb9\u6570\u636e\u6700\u5c0f\uff0c\u53f3\u8fb9\u6570\u636e\u6700\u5927\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>6\uff09B+\u6811\u56fe\u793a\u8bf4\u660e<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">MySQL\u4e2d\u7d22\u5f15\u4f7f\u7528\u7684\u5c31\u662fB+\u6811\u7ed3\u6784\u3002<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005456568.jpeg\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5716535433070866\" data-type=\"jpeg\" data-w=\"635\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005456568.jpeg\" data-ratio=\"0.5716535433070866\" data-type=\"jpeg\" data-w=\"635\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5173\u4e8eB+\u6811\u7684\u8bf4\u660e\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u9996\u5148\uff0cBtree\u4e00\u822c\u6307\u7684\u90fd\u662f\u3010B+\u6811\u3011\uff0c\u6570\u636e\u5168\u90e8\u5b58\u653e\u5728\u53f6\u5b50\u8282\u70b9\u4e2d\u3002\u5bf9\u4e8e\u4e0a\u56fe\u6765\u8bf4\uff0c\u6700\u4e0b\u9762\u7684\u7b2c3\u5c42\uff0c\u5c5e\u4e8e\u53f6\u5b50\u8282\u70b9\uff0c\u771f\u5b9e\u6570\u636e\u90e8\u4efd\u90fd\u662f\u5b58\u653e\u5728\u53f6\u5b50\u8282\u70b9\u5f53\u4e2d\u7684\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u90a3\u4e48\u5bf9\u4e8e\u7b2c1\u30012\u5c42\u4e2d\u7684\u6570\u636e\u53c8\u662f\u5e72\u561b\u7684\u5462\uff1f\u7b54\uff1a\u7528\u4e8e\u5206\u5272\u6307\u9488\u5757\u513f\u7684\uff0c\u6bd4\u5982\u8bf4\u5c0f\u4e8e26\u7684\u627eP1\uff0c\u4ecb\u4e8e26-30\u4e4b\u95f4\u7684\u627eP2\uff0c\u5927\u4e8e30\u7684\u627eP3\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5176\u6b21\uff0c\u4e09\u5c42\u3010B+\u6811\u3011\u53ef\u4ee5\u5b58\u653e\u4e0a\u767e\u4e07\u6761\u6570\u636e\u3002\u8fd9\u4e48\u591a\u6570\u636e\u600e\u4e48\u653e\u7684\u5462\uff1f\u589e\u52a0\u201c\u8282\u70b9\u6570\u201d\u3002\u56fe\u4e2d\u6211\u4eec\u53ea\u6709\u4e09\u4e2a\u8282\u70b9\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6700\u540e\uff0c\u3010B+\u6811\u3011\u4e2d\u67e5\u8be2\u4efb\u610f\u6570\u636e\u7684\u6b21\u6570\uff0c\u90fd\u662fn\u6b21\uff0cn\u8868\u793a\u7684\u662f\u3010B+\u6811\u3011\u7684\u9ad8\u5ea6\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\u3001\u7d22\u5f15\u7684\u5206\u7c7b\u4e0e\u521b\u5efa<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09\u7d22\u5f15\u5206\u7c7b<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5355\u503c\u7d22\u5f15<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u552f\u4e00\u7d22\u5f15<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u590d\u5408\u7d22\u5f15<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u5355\u503c\u7d22\u5f15<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5229\u7528\u8868\u4e2d\u7684\u67d0\u4e00\u4e2a\u5b57\u6bb5\u521b\u5efa\u5355\u503c\u7d22\u5f15\u3002\u4e00\u5f20\u8868\u4e2d\u5f80\u5f80\u6709\u591a\u4e2a\u5b57\u6bb5\uff0c\u4e5f\u5c31\u662f\u8bf4\u6bcf\u4e00\u5217\u5176\u5b9e\u90fd\u53ef\u4ee5\u521b\u5efa\u4e00\u4e2a\u7d22\u5f15\uff0c\u8fd9\u4e2a\u6839\u636e\u6211\u4eec\u5b9e\u9645\u9700\u6c42\u6765\u8fdb\u884c\u521b\u5efa\u3002\u8fd8\u9700\u8981\u6ce8\u610f\u7684\u4e00\u70b9\u5c31\u662f\uff0c\u4e00\u5f20\u8868\u53ef\u4ee5\u521b\u5efa\u591a\u4e2a\u201c\u5355\u503c\u7d22\u5f15\u201d\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5047\u5982\u67d0\u4e00\u5f20\u8868\u65e2\u6709age\u5b57\u6bb5\uff0c\u53c8\u6709name\u5b57\u6bb5\uff0c\u6211\u4eec\u53ef\u4ee5\u5206\u522b\u5bf9age\u3001name\u521b\u5efa\u4e00\u4e2a\u5355\u503c\u7d22\u5f15\uff0c\u8fd9\u6837\u4e00\u5f20\u8868\u5c31\u6709\u4e86\u4e24\u4e2a\u5355\u503c\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u552f\u4e00\u7d22\u5f15<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e5f\u662f\u5229\u7528\u8868\u4e2d\u7684\u67d0\u4e00\u4e2a\u5b57\u6bb5\u521b\u5efa\u5355\u503c\u7d22\u5f15\uff0c\u4e0e\u5355\u503c\u7d22\u5f15\u4e0d\u540c\u7684\u662f\uff1a\u521b\u5efa\u552f\u4e00\u7d22\u5f15\u7684\u5b57\u6bb5\u4e2d\u7684\u6570\u636e\uff0c\u4e0d\u80fd\u6709\u91cd\u590d\u503c\u3002\u50cfage\u80af\u5b9a\u6709\u5f88\u591a\u4eba\u7684\u5e74\u9f84\u76f8\u540c\uff0c\u50cfname\u80af\u5b9a\u6709\u4e9b\u4eba\u662f\u91cd\u540d\u7684\uff0c\u56e0\u6b64\u90fd\u4e0d\u9002\u5408\u521b\u5efa\u201c\u552f\u4e00\u7d22\u5f15\u201d\u3002\u50cf\u7f16\u53f7id\u3001\u5b66\u53f7sid\uff0c\u5bf9\u4e8e\u6bcf\u4e2a\u4eba\u90fd\u4e0d\u4e00\u6837\uff0c\u56e0\u6b64\u53ef\u4ee5\u7528\u4e8e\u521b\u5efa\u552f\u4e00\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 \u590d\u5408\u7d22\u5f15<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u591a\u4e2a\u5217\u5171\u540c\u6784\u6210\u7684\u7d22\u5f15\u3002\u6bd4\u5982\u8bf4\u6211\u4eec\u521b\u5efa\u8fd9\u6837\u4e00\u4e2a\u201c\u590d\u5408\u7d22\u5f15\u201d(name,age)\uff0c\u5148\u5229\u7528name\u8fdb\u884c\u7d22\u5f15\u67e5\u8be2\uff0c\u5f53name\u76f8\u540c\u7684\u65f6\u5019\uff0c\u6211\u4eec\u5229\u7528age\u518d\u8fdb\u884c\u4e00\u6b21\u7b5b\u9009\u3002\u6ce8\u610f\uff1a\u590d\u5408\u7d22\u5f15\u7684\u5b57\u6bb5\u5e76\u4e0d\u662f\u975e\u8981\u90fd\u7528\u5b8c\uff0c\u5f53\u6211\u4eec\u5229\u7528name\u5b57\u6bb5\u7d22\u5f15\u51fa\u6211\u4eec\u60f3\u8981\u7684\u7ed3\u679c\u4ee5\u540e\uff0c\u5c31\u4e0d\u9700\u8981\u518d\u4f7f\u7528age\u8fdb\u884c\u518d\u6b21\u7b5b\u9009\u4e86\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09\u521b\u5efa\u7d22\u5f15<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u8bed\u6cd5<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8bed\u6cd5\uff1acreate \u7d22\u5f15\u7c7b\u578b \u7d22\u5f15\u540d on \u8868(\u5b57\u6bb5);<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5efa\u8868\u8bed\u53e5\u5982\u4e0b\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u67e5\u8be2\u8868\u7ed3\u6784\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005457970.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.3812785388127854\" data-type=\"png\" data-w=\"438\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005457970.png\" data-ratio=\"0.3812785388127854\" data-type=\"png\" data-w=\"438\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u521b\u5efa\u7d22\u5f15\u7684\u7b2c\u4e00\u79cd\u65b9\u5f0f<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2160 \u521b\u5efa\u5355\u503c\u7d22\u5f15<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">create\u00a0index\u00a0dept_index\u00a0on\u00a0tb(dept);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2161 \u521b\u5efa\u552f\u4e00\u7d22\u5f15\uff1a\u8fd9\u91cc\u6211\u4eec\u5047\u5b9aname\u5b57\u6bb5\u4e2d\u7684\u503c\u90fd\u662f\u552f\u4e00\u7684<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">create\u00a0unique\u00a0index\u00a0name_index\u00a0on\u00a0tb(name);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2162 \u521b\u5efa\u590d\u5408\u7d22\u5f15<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">create\u00a0index\u00a0dept_name_index\u00a0on\u00a0tb(dept,name);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 \u521b\u5efa\u7d22\u5f15\u7684\u7b2c\u4e8c\u79cd\u65b9\u5f0f<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5148\u5220\u9664\u4e4b\u524d\u521b\u5efa\u7684\u7d22\u5f15\u4ee5\u540e\uff0c\u518d\u8fdb\u884c\u8fd9\u79cd\u521b\u5efa\u7d22\u5f15\u65b9\u5f0f\u7684\u6d4b\u8bd5\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u8bed\u6cd5\uff1aalter table \u8868\u540d add \u7d22\u5f15\u7c7b\u578b \u7d22\u5f15\u540d(\u5b57\u6bb5)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2160 \u521b\u5efa\u5355\u503c\u7d22\u5f15<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">alter\u00a0table\u00a0tb\u00a0add\u00a0index\u00a0dept_index(dept);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2161 \u521b\u5efa\u552f\u4e00\u7d22\u5f15\uff1a\u8fd9\u91cc\u6211\u4eec\u5047\u5b9aname\u5b57\u6bb5\u4e2d\u7684\u503c\u90fd\u662f\u552f\u4e00\u7684<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">alter\u00a0table\u00a0tb\u00a0add\u00a0unique\u00a0index\u00a0name_index(name);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u2162 \u521b\u5efa\u590d\u5408\u7d22\u5f15<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">alter\u00a0table\u00a0tb\u00a0add\u00a0index\u00a0dept_name_index(dept,name);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 \u8865\u5145\u8bf4\u660e<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5982\u679c\u67d0\u4e2a\u5b57\u6bb5\u662fprimary key\uff0c\u90a3\u4e48\u8be5\u5b57\u6bb5\u9ed8\u8ba4\u5c31\u662f\u4e3b\u952e\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e3b\u952e\u7d22\u5f15\u548c\u552f\u4e00\u7d22\u5f15\u975e\u5e38\u76f8\u4f3c\u3002\u76f8\u540c\u70b9\uff1a\u8be5\u5217\u4e2d\u7684\u6570\u636e\u90fd\u4e0d\u80fd\u6709\u76f8\u540c\u503c\uff1b\u4e0d\u540c\u70b9\uff1a\u4e3b\u952e\u7d22\u5f15\u4e0d\u80fd\u6709null\u503c\uff0c\u4f46\u662f\u552f\u4e00\u7d22\u5f15\u53ef\u4ee5\u6709null\u503c\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\uff09\u7d22\u5f15\u5220\u9664\u548c\u7d22\u5f15\u67e5\u8be2<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u7d22\u5f15\u5220\u9664<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8bed\u6cd5\uff1adrop index \u7d22\u5f15\u540d on \u8868\u540d;<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">drop\u00a0index\u00a0name_index\u00a0on\u00a0tb;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u7d22\u5f15\u67e5\u8be2<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8bed\u6cd5\uff1ashow index from \u8868\u540d;<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">show\u00a0index\u00a0from\u00a0tb;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005458175.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.22954303931987247\" data-type=\"png\" data-w=\"941\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005458175.png\" data-ratio=\"0.22954303931987247\" data-type=\"png\" data-w=\"941\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>4\u3001SQL\u6027\u80fd\u95ee\u9898\u7684\u63a2\u7d22<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u4eba\u4e3a\u4f18\u5316\uff1a<\/strong> \u9700\u8981\u6211\u4eec\u4f7f\u7528explain\u5206\u6790SQL\u7684\u6267\u884c\u8ba1\u5212\u3002\u8be5\u6267\u884c\u8ba1\u5212\u53ef\u4ee5\u6a21\u62dfSQL\u4f18\u5316\u5668\u6267\u884cSQL\u8bed\u53e5\uff0c\u53ef\u4ee5\u5e2e\u52a9\u6211\u4eec\u4e86\u89e3\u5230\u81ea\u5df1\u7f16\u5199SQL\u7684\u597d\u574f\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>SQL\u4f18\u5316\u5668\u81ea\u52a8\u4f18\u5316\uff1a<\/strong> \u6700\u5f00\u59cb\u8bb2\u8ff0MySQL\u6267\u884c\u539f\u7406\u7684\u65f6\u5019\uff0c\u6211\u4eec\u5df2\u7ecf\u77e5\u9053MySQL\u6709\u4e00\u4e2a\u4f18\u5316\u5668\uff0c\u5f53\u4f60\u5199\u4e86\u4e00\u4e2aSQL\u8bed\u53e5\u7684\u65f6\u5019\uff0cSQL\u4f18\u5316\u5668\u5982\u679c\u8ba4\u4e3a\u4f60\u5199\u7684SQL\u8bed\u53e5\u4e0d\u591f\u597d\uff0c\u5c31\u4f1a\u81ea\u52a8\u5199\u4e00\u4e2a\u597d\u4e00\u4e9b\u7684\u7b49\u4ef7SQL\u53bb\u6267\u884c\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">SQL\u4f18\u5316\u5668\u81ea\u52a8\u4f18\u5316\u529f\u80fd\u3010\u4f1a\u5e72\u6270\u3011\u6211\u4eec\u7684\u4eba\u4e3a\u4f18\u5316\u529f\u80fd\u3002\u5f53\u6211\u4eec\u67e5\u770b\u4e86SQL\u6267\u884c\u8ba1\u5212\u4ee5\u540e\uff0c\u5982\u679c\u5199\u7684\u4e0d\u597d\uff0c\u6211\u4eec\u4f1a\u53bb\u4f18\u5316\u81ea\u5df1\u7684SQL\u3002\u5f53\u6211\u4eec\u4ee5\u4e3a\u81ea\u5df1\u4f18\u5316\u7684\u5f88\u597d\u7684\u65f6\u5019\uff0c\u6700\u7ec8\u7684\u6267\u884c\u8ba1\u5212\uff0c\u5e76\u4e0d\u662f\u6309\u7167\u6211\u4eec\u4f18\u5316\u597d\u7684SQL\u8bed\u53e5\u6765\u6267\u884c\u7684\uff0c\u800c\u662f\u6709\u65f6\u5019\u5c06\u6211\u4eec\u4f18\u5316\u597d\u7684SQL\u6539\u53d8\u4e86\uff0c\u53bb\u6267\u884c\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">SQL\u4f18\u5316\u662f\u4e00\u79cd\u6982\u7387\u95ee\u9898\uff0c\u6709\u65f6\u5019\u7cfb\u7edf\u4f1a\u6309\u7167\u6211\u4eec\u4f18\u5316\u597d\u7684SQL\u53bb\u6267\u884c\u7ed3\u679c(\u4f18\u5316\u5668\u89c9\u5f97\u4f60\u5199\u7684\u5dee\u4e0d\u591a\uff0c\u5c31\u4e0d\u4f1a\u52a8\u4f60\u7684SQL)\u3002\u6709\u65f6\u5019\u4f18\u5316\u5668\u4ecd\u7136\u4f1a\u4fee\u6539\u6211\u4eec\u4f18\u5316\u597d\u7684SQL\uff0c\u7136\u540e\u518d\u53bb\u6267\u884c\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8bed\u6cd5\uff1aexplain + SQL\u8bed\u53e5<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">eg\uff1aexplain select * from tb;<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09\u201c\u6267\u884c\u8ba1\u5212\u201d\u4e2d\u9700\u8981\u77e5\u9053\u7684\u51e0\u4e2a\u201c\u5173\u952e\u5b57\u201d<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">id \uff1a\u7f16\u53f7<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">select_type \uff1a\u67e5\u8be2\u7c7b\u578b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">table \uff1a\u8868<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">type \uff1a\u7c7b\u578b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">possible_keys \uff1a\u9884\u6d4b\u7528\u5230\u7684\u7d22\u5f15<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">key \uff1a\u5b9e\u9645\u4f7f\u7528\u7684\u7d22\u5f15<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">key_len \uff1a\u5b9e\u9645\u4f7f\u7528\u7d22\u5f15\u7684\u957f\u5ea6<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">ref \uff1a\u8868\u4e4b\u95f4\u7684\u5f15\u7528<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">rows \uff1a\u901a\u8fc7\u7d22\u5f15\u67e5\u8be2\u5230\u7684\u6570\u636e\u91cf<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">Extra \uff1a\u989d\u5916\u7684\u4fe1\u606f<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u5efa\u8868\u8bed\u53e5\u548c\u63d2\u5165\u6570\u636e\uff1a<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5efa\u8868\u8bed\u53e5<\/span>\ncreate\u00a0table\u00a0course\n(\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0cid\u00a0int(3),\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0cname\u00a0varchar(20),\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tid\u00a0int(3)\n);\n\ncreate\u00a0table\u00a0teacher\n(\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tid\u00a0int(3),\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tname\u00a0varchar(20),\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tcid\u00a0int(3)\n);\n\ncreate\u00a0table\u00a0teacherCard\n(\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tcid\u00a0int(3),\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tcdesc\u00a0varchar(200)\n);\n\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u63d2\u5165\u6570\u636e<\/span>\ninsert\u00a0into\u00a0course\u00a0values(1,<span style=\"color: #98c379; line-height: 26px;\">'java'<\/span>,1);\ninsert\u00a0into\u00a0course\u00a0values(2,<span style=\"color: #98c379; line-height: 26px;\">'html'<\/span>,1);\ninsert\u00a0into\u00a0course\u00a0values(3,<span style=\"color: #98c379; line-height: 26px;\">'sql'<\/span>,2);\ninsert\u00a0into\u00a0course\u00a0values(4,<span style=\"color: #98c379; line-height: 26px;\">'web'<\/span>,3);\n\ninsert\u00a0into\u00a0teacher\u00a0values(1,<span style=\"color: #98c379; line-height: 26px;\">'tz'<\/span>,1);\ninsert\u00a0into\u00a0teacher\u00a0values(2,<span style=\"color: #98c379; line-height: 26px;\">'tw'<\/span>,2);\ninsert\u00a0into\u00a0teacher\u00a0values(3,<span style=\"color: #98c379; line-height: 26px;\">'tl'<\/span>,3);\n\ninsert\u00a0into\u00a0teacherCard\u00a0values(1,<span style=\"color: #98c379; line-height: 26px;\">'tzdesc'<\/span>)\u00a0;\ninsert\u00a0into\u00a0teacherCard\u00a0values(2,<span style=\"color: #98c379; line-height: 26px;\">'twdesc'<\/span>)\u00a0;\ninsert\u00a0into\u00a0teacherCard\u00a0values(3,<span style=\"color: #98c379; line-height: 26px;\">'tldesc'<\/span>)\u00a0;\n<\/code><\/pre>\n<h1 style=\"margin-bottom: 15px; font-weight: bold; font-size: 24px; margin-top: 16px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><span style=\"font-size: 18px;\">explain\u6267\u884c\u8ba1\u5212\u5e38\u7528\u5173\u952e\u5b57\u8be6\u89e3<\/span><\/h1>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09id\u5173\u952e\u5b57\u7684\u4f7f\u7528\u8bf4\u660e<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u6848\u4f8b\uff1a\u67e5\u8be2\u8bfe\u7a0b\u7f16\u53f7\u4e3a2 \u6216 \u6559\u5e08\u8bc1\u7f16\u53f7\u4e3a3 \u7684\u8001\u5e08\u4fe1\u606f\uff1a<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0t.*\nfrom\u00a0teacher\u00a0t,course\u00a0c,teacherCard\u00a0tc\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tid\u00a0=\u00a0c.tid\u00a0and\u00a0t.tcid\u00a0=\u00a0tc.tcid\nand\u00a0(c.cid\u00a0=\u00a02\u00a0or\u00a0tc.tcid\u00a0=\u00a03);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005459956.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.1301518438177874\" data-type=\"png\" data-w=\"922\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005459956.png\" data-ratio=\"0.1301518438177874\" data-type=\"png\" data-w=\"922\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u63a5\u7740\uff0c\u5728\u5f80teacher\u8868\u4e2d\u589e\u52a0\u51e0\u6761\u6570\u636e\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">insert\u00a0into\u00a0teacher\u00a0values(4,<span style=\"color: #98c379; line-height: 26px;\">'ta'<\/span>,4);\ninsert\u00a0into\u00a0teacher\u00a0values(5,<span style=\"color: #98c379; line-height: 26px;\">'tb'<\/span>,5);\ninsert\u00a0into\u00a0teacher\u00a0values(6,<span style=\"color: #98c379; line-height: 26px;\">'tc'<\/span>,6);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u518d\u6b21\u67e5\u770b\u6267\u884c\u8ba1\u5212\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0t.*\nfrom\u00a0teacher\u00a0t,course\u00a0c,teacherCard\u00a0tc\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tid\u00a0=\u00a0c.tid\u00a0and\u00a0t.tcid\u00a0=\u00a0tc.tcid\nand\u00a0(c.cid\u00a0=\u00a02\u00a0or\u00a0tc.tcid\u00a0=\u00a03);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005500140.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.16251638269986893\" data-type=\"png\" data-w=\"763\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005500140.png\" data-ratio=\"0.16251638269986893\" data-type=\"png\" data-w=\"763\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8868\u7684\u6267\u884c\u987a\u5e8f \uff0c\u56e0\u8868\u6570\u91cf\u6539\u53d8\u800c\u6539\u53d8\u7684\u539f\u56e0\uff1a\u7b1b\u5361\u5c14\u79ef\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">a\u00a0\u00a0\u00a0b\u00a0\u00a0\u00a0c\n2\u00a0\u00a0\u00a03\u00a0\u00a0\u00a04\n\u6700\u7ec8\uff1a2 * 3 * 4 \u00a0= 6 * 4 = 24\nc\u00a0\u00a0\u00a0b\u00a0\u00a0\u00a0a\n4\u00a0\u00a0\u00a03\u00a0\u00a0\u00a02\n\u6700\u7ec8\uff1a4 * 3 * 2 = 12 * 2 = 24\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5206\u6790\uff1a\u6700\u7ec8\u6267\u884c\u7684\u6761\u6570\uff0c\u867d\u7136\u662f\u4e00\u81f4\u7684\u3002\u4f46\u662f\u4e2d\u95f4\u8fc7\u7a0b\uff0c\u6709\u4e00\u5f20\u4e34\u65f6\u8868\u662f6\uff0c\u4e00\u5f20\u4e34\u65f6\u8868\u662f12\uff0c\u5f88\u660e\u663e6 &lt; 12\uff0c\u5bf9\u4e8e\u5185\u5b58\u6765\u8bf4\uff0c\u6570\u636e\u91cf\u8d8a\u5c0f\u8d8a\u597d\uff0c\u56e0\u6b64\u4f18\u5316\u5668\u80af\u5b9a\u4f1a\u9009\u62e9\u7b2c\u4e00\u79cd\u6267\u884c\u987a\u5e8f\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u8bba\uff1aid\u503c\u76f8\u540c\uff0c\u4ece\u4e0a\u5f80\u4e0b\u987a\u5e8f\u6267\u884c\u3002\u8868\u7684\u6267\u884c\u987a\u5e8f\u56e0\u8868\u6570\u91cf\u7684\u6539\u53d8\u800c\u6539\u53d8\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u6848\u4f8b\uff1a\u67e5\u8be2\u6559\u6388SQL\u8bfe\u7a0b\u7684\u8001\u5e08\u7684\u63cf\u8ff0(desc)<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0tc.tcdesc\u00a0from\u00a0teacherCard\u00a0tc\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tc.tcid\u00a0=\u00a0\n(\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0select\u00a0t.tcid\u00a0from\u00a0teacher\u00a0t\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0\u00a0t.tid\u00a0=\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0(select\u00a0c.tid\u00a0from\u00a0course\u00a0c\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.cname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'sql'<\/span>)\n);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005501631.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.13631406761177753\" data-type=\"png\" data-w=\"917\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005501631.png\" data-ratio=\"0.13631406761177753\" data-type=\"png\" data-w=\"917\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u8bba\uff1aid\u503c\u4e0d\u540c\uff0cid\u503c\u8d8a\u5927\u8d8a\u4f18\u5148\u67e5\u8be2\u3002\u8fd9\u662f\u7531\u4e8e\u5728\u8fdb\u884c\u5d4c\u5957\u5b50\u67e5\u8be2\u65f6\uff0c\u5148\u67e5\u5185\u5c42\uff0c\u518d\u67e5\u5916\u5c42\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 \u9488\u5bf9\u2461\u505a\u4e00\u4e2a\u7b80\u5355\u7684\u4fee\u6539<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0t.tname\u00a0,tc.tcdesc\u00a0from\u00a0teacher\u00a0t,teacherCard\u00a0tc\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tcid=\u00a0tc.tcid\nand\u00a0t.tid\u00a0=\u00a0(select\u00a0c.tid\u00a0from\u00a0course\u00a0c\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0cname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'sql'<\/span>)\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005502843.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.13034188034188035\" data-type=\"png\" data-w=\"936\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005502843.png\" data-ratio=\"0.13034188034188035\" data-type=\"png\" data-w=\"936\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u8bba\uff1aid\u503c\u6709\u76f8\u540c\uff0c\u53c8\u6709\u4e0d\u540c\u3002id\u503c\u8d8a\u5927\u8d8a\u4f18\u5148\uff1bid\u503c\u76f8\u540c\uff0c\u4ece\u4e0a\u5f80\u4e0b\u987a\u5e8f\u6267\u884c\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09select_type\u5173\u952e\u5b57\u7684\u4f7f\u7528\u8bf4\u660e\uff1a\u67e5\u8be2\u7c7b\u578b<\/strong><\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"lazyload\"style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 174px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005503129.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.8908045977011494\" data-type=\"png\" data-w=\"174\" \/><noscript><img decoding=\"async\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 174px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005503129.png\" data-ratio=\"0.8908045977011494\" data-type=\"png\" data-w=\"174\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 simple\uff1a\u7b80\u5355\u67e5\u8be2<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e0d\u5305\u542b\u5b50\u67e5\u8be2\uff0c\u4e0d\u5305\u542bunion\u67e5\u8be2\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0teacher;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005503634.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.14097968936678615\" data-type=\"png\" data-w=\"837\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005503634.png\" data-ratio=\"0.14097968936678615\" data-type=\"png\" data-w=\"837\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 primary\uff1a\u5305\u542b\u5b50\u67e5\u8be2\u7684\u4e3b\u67e5\u8be2(\u6700\u5916\u5c42)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 subquery\uff1a\u5305\u542b\u5b50\u67e5\u8be2\u7684\u4e3b\u67e5\u8be2(\u975e\u6700\u5916\u5c42)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 derived\uff1a\u884d\u751f\u67e5\u8be2(\u7528\u5230\u4e86\u4e34\u65f6\u8868)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">a.\u5728from\u5b50\u67e5\u8be2\u4e2d\uff0c\u53ea\u6709\u4e00\u5f20\u8868\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">b.\u5728from\u5b50\u67e5\u8be2\u4e2d\uff0c\u5982\u679ctable1 union table2\uff0c\u5219table1\u5c31\u662fderived\u8868\uff1b<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0\u00a0cr.cname\u00a0\u00a0\u00a0\u00a0\nfrom\u00a0(\u00a0select\u00a0*\u00a0from\u00a0course\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tid\u00a0=\u00a01\u00a0\u00a0union\u00a0select\u00a0*\u00a0from\u00a0course\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tid\u00a0=\u00a02\u00a0)\u00a0cr\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005504405.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.16609783845278725\" data-type=\"png\" data-w=\"879\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005504405.png\" data-ratio=\"0.16609783845278725\" data-type=\"png\" data-w=\"879\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2464 union\uff1aunion\u4e4b\u540e\u7684\u8868\u79f0\u4e4b\u4e3aunion\u8868\uff0c\u5982\u4e0a\u4f8b<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2465 union result\uff1a\u544a\u8bc9\u6211\u4eec\uff0c\u54ea\u4e9b\u8868\u4e4b\u95f4\u4f7f\u7528\u4e86union\u67e5\u8be2<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\uff09type\u5173\u952e\u5b57\u7684\u4f7f\u7528\u8bf4\u660e\uff1a\u7d22\u5f15\u7c7b\u578b<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">system\u3001const\u53ea\u662f\u7406\u60f3\u72b6\u51b5\uff0c\u5b9e\u9645\u4e0a\u53ea\u80fd\u4f18\u5316\u5230index --&gt; range --&gt; ref\u8fd9\u4e2a\u7ea7\u522b\u3002\u8981\u5bf9type\u8fdb\u884c\u4f18\u5316\u7684\u524d\u63d0\u662f\uff0c\u4f60\u5f97\u521b\u5efa\u7d22\u5f15\u3002<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 479px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005505950.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.0918580375782881\" data-type=\"png\" data-w=\"479\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 479px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005505950.png\" data-ratio=\"0.0918580375782881\" data-type=\"png\" data-w=\"479\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 system<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6e90\u8868\u53ea\u6709\u4e00\u6761\u6570\u636e(\u5b9e\u9645\u4e2d\uff0c\u57fa\u672c\u4e0d\u53ef\u80fd)\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u884d\u751f\u8868\u53ea\u6709\u4e00\u6761\u6570\u636e\u7684\u4e3b\u67e5\u8be2(\u5076\u5c14\u53ef\u4ee5\u8fbe\u5230)\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 const<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4ec5\u4ec5\u80fd\u67e5\u5230\u4e00\u6761\u6570\u636e\u7684SQL ,\u4ec5\u9488\u5bf9Primary key\u6216unique\u7d22\u5f15\u7c7b\u578b\u6709\u6548\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0tid\u00a0from\u00a0test01\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tid\u00a0=1\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005506818.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.1356297093649085\" data-type=\"png\" data-w=\"929\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005506818.png\" data-ratio=\"0.1356297093649085\" data-type=\"png\" data-w=\"929\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5220\u9664\u4ee5\u524d\u7684\u4e3b\u952e\u7d22\u5f15\u540e\uff0c\u6b64\u65f6\u6211\u4eec\u6dfb\u52a0\u4e00\u4e2a\u5176\u4ed6\u7684\u666e\u901a\u7d22\u5f15\uff1a<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">create\u00a0index\u00a0test01_index\u00a0on\u00a0test01(tid)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u518d\u6b21\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0tid\u00a0from\u00a0test01\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tid\u00a0=1\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005506397.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.12134344528710726\" data-type=\"png\" data-w=\"923\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005506397.png\" data-ratio=\"0.12134344528710726\" data-type=\"png\" data-w=\"923\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 eq_ref<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u552f\u4e00\u6027\u7d22\u5f15\uff0c\u5bf9\u4e8e\u6bcf\u4e2a\u7d22\u5f15\u952e\u7684\u67e5\u8be2\uff0c\u8fd4\u56de\u5339\u914d\u552f\u4e00\u884c\u6570\u636e\uff08\u6709\u4e14\u53ea\u67091\u4e2a\uff0c\u4e0d\u80fd\u591a \u3001\u4e0d\u80fd0\uff09\uff0c\u5e76\u4e14\u67e5\u8be2\u7ed3\u679c\u548c\u6570\u636e\u6761\u6570\u5fc5\u987b\u4e00\u81f4\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6b64\u79cd\u60c5\u51b5\u5e38\u89c1\u4e8e\u552f\u4e00\u7d22\u5f15\u548c\u4e3b\u952e\u7d22\u5f15\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">delete\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tcid\u00a0&gt;=\u00a04;\nalter\u00a0table\u00a0teacherCard\u00a0add\u00a0constraint\u00a0pk_tcid\u00a0primary\u00a0key(tcid);\nalter\u00a0table\u00a0teacher\u00a0add\u00a0constraint\u00a0uk_tcid\u00a0unique\u00a0index(tcid)\u00a0;\nexplain\u00a0select\u00a0t.tcid\u00a0from\u00a0teacher\u00a0t,teacherCard\u00a0tc\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tcid\u00a0=\u00a0tc.tcid\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005507943.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.14776274713839752\" data-type=\"png\" data-w=\"961\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005507943.png\" data-ratio=\"0.14776274713839752\" data-type=\"png\" data-w=\"961\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u603b\u7ed3\uff1a\u4ee5\u4e0aSQL\uff0c\u7528\u5230\u7684\u7d22\u5f15\u662ft.tcid\uff0c\u5373teacher\u8868\u4e2d\u7684tcid\u5b57\u6bb5\uff1b\u5982\u679cteacher\u8868\u7684\u6570\u636e\u4e2a\u6570\u548c\u8fde\u63a5\u67e5\u8be2\u7684\u6570\u636e\u4e2a\u6570\u4e00\u81f4\uff08\u90fd\u662f3\u6761\u6570\u636e\uff09\uff0c\u5219\u6709\u53ef\u80fd\u6ee1\u8db3eq_ref\u7ea7\u522b\uff1b\u5426\u5219\u65e0\u6cd5\u6ee1\u8db3\u3002\u6761\u4ef6\u5f88\u82db\u523b\uff0c\u5f88\u96be\u8fbe\u5230\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 ref<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u975e\u552f\u4e00\u6027\u7d22\u5f15\uff0c\u5bf9\u4e8e\u6bcf\u4e2a\u7d22\u5f15\u952e\u7684\u67e5\u8be2\uff0c\u8fd4\u56de\u5339\u914d\u7684\u6240\u6709\u884c\uff08\u53ef\u4ee50\uff0c\u53ef\u4ee51\uff0c\u53ef\u4ee5\u591a\uff09<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u51c6\u5907\u6570\u636e\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 400px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005508845.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"1.0975\" data-type=\"png\" data-w=\"400\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 400px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005508845.png\" data-ratio=\"1.0975\" data-type=\"png\" data-w=\"400\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u521b\u5efa\u7d22\u5f15\uff0c\u5e76\u67e5\u770b\u6267\u884c\u8ba1\u5212\uff1a<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u6dfb\u52a0\u7d22\u5f15<\/span>\nalter\u00a0table\u00a0teacher\u00a0add\u00a0index\u00a0index_name\u00a0(tname)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0\u00a0\u00a0\u00a0\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'tz'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005509622.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.13149171270718232\" data-type=\"png\" data-w=\"905\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005509622.png\" data-ratio=\"0.13149171270718232\" data-type=\"png\" data-w=\"905\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2464 range<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u68c0\u7d22\u6307\u5b9a\u8303\u56f4\u7684\u884c ,where\u540e\u9762\u662f\u4e00\u4e2a\u8303\u56f4\u67e5\u8be2(between, &gt;, &lt;, &gt;=, in)<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">in\u6709\u65f6\u5019\u4f1a\u5931\u6548\uff0c\u4ece\u800c\u8f6c\u4e3a\u65e0\u7d22\u5f15\u65f6\u5019\u7684ALL<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u6dfb\u52a0\u7d22\u5f15<\/span>\nalter\u00a0table\u00a0teacher\u00a0add\u00a0index\u00a0tid_index\u00a0(tid)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212\uff1a\u4ee5\u4e0b\u5199\u4e86\u4e00\u79cd\u7b49\u4ef7SQL\u5199\u6cd5\uff0c\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0t.*\u00a0from\u00a0teacher\u00a0t\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tid\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>\u00a0(1,2)\u00a0;\nexplain\u00a0select\u00a0t.*\u00a0from\u00a0teacher\u00a0t\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tid\u00a0&lt;3\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005510403.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.3111111111111111\" data-type=\"png\" data-w=\"1080\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005510403.png\" data-ratio=\"0.3111111111111111\" data-type=\"png\" data-w=\"1080\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2465 index<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u67e5\u8be2\u5168\u90e8\u7d22\u5f15\u4e2d\u7684\u6570\u636e(\u626b\u63cf\u6574\u4e2a\u7d22\u5f15)<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2466 ALL<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u67e5\u8be2\u5168\u90e8\u6e90\u8868\u4e2d\u7684\u6570\u636e(\u66b4\u529b\u626b\u63cf\u5168\u8868)<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005512763.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5416267942583732\" data-type=\"png\" data-w=\"1045\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005512763.png\" data-ratio=\"0.5416267942583732\" data-type=\"png\" data-w=\"1045\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6ce8\u610f\uff1acid\u662f\u7d22\u5f15\u5b57\u6bb5\uff0c\u56e0\u6b64\u67e5\u8be2\u7d22\u5f15\u5b57\u6bb5\uff0c\u53ea\u9700\u8981\u626b\u63cf\u7d22\u5f15\u8868\u5373\u53ef\u3002\u4f46\u662ftid\u4e0d\u662f\u7d22\u5f15\u5b57\u6bb5\uff0c\u67e5\u8be2\u975e\u7d22\u5f15\u5b57\u6bb5\uff0c\u9700\u8981\u66b4\u529b\u626b\u63cf\u6574\u4e2a\u6e90\u8868\uff0c\u4f1a\u6d88\u8017\u66f4\u591a\u7684\u8d44\u6e90\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>4\uff09possible_keys\u548ckey<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">possible_keys\u53ef\u80fd\u7528\u5230\u7684\u7d22\u5f15\u3002\u662f\u4e00\u79cd\u9884\u6d4b\uff0c\u4e0d\u51c6\u3002\u4e86\u89e3\u4e00\u4e0b\u5c31\u597d\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">key\u6307\u7684\u662f\u5b9e\u9645\u4f7f\u7528\u7684\u7d22\u5f15\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5148\u7ed9course\u8868\u7684cname\u5b57\u6bb5\uff0c\u6dfb\u52a0\u4e00\u4e2a\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0cname_index\u00a0on\u00a0course(cname);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0t.tname\u00a0,tc.tcdesc\u00a0from\u00a0teacher\u00a0t,teacherCard\u00a0tc\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0t.tcid=\u00a0tc.tcid\nand\u00a0t.tid\u00a0=\u00a0(select\u00a0c.tid\u00a0from\u00a0course\u00a0c\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0cname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'sql'<\/span>)\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005515754.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.18500948766603414\" data-type=\"png\" data-w=\"1054\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005515754.png\" data-ratio=\"0.18500948766603414\" data-type=\"png\" data-w=\"1054\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6709\u4e00\u70b9\u9700\u8981\u6ce8\u610f\u7684\u662f\uff1a\u5982\u679cpossible_key\/key\u662fNULL\uff0c\u5219\u8bf4\u660e\u6ca1\u7528\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>5\uff09key_len<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7d22\u5f15\u7684\u957f\u5ea6\uff0c\u7528\u4e8e\u5224\u65ad\u590d\u5408\u7d22\u5f15\u662f\u5426\u88ab\u5b8c\u5168\u4f7f\u7528(a,b,c)\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u65b0\u5efa\u4e00\u5f20\u65b0\u8868\uff0c\u7528\u4e8e\u6d4b\u8bd5<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u8868<\/span>\ncreate\u00a0table\u00a0test_kl\n(\u00a0\u00a0\n\u00a0\u00a0name\u00a0char(20)\u00a0not\u00a0null\u00a0default\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u6dfb\u52a0\u7d22\u5f15<\/span>\nalter\u00a0table\u00a0test_kl\u00a0add\u00a0index\u00a0index_name(name)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0test_kl\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0name\u00a0=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005516303.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.3702064896755162\" data-type=\"png\" data-w=\"678\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005516303.png\" data-ratio=\"0.3702064896755162\" data-type=\"png\" data-w=\"678\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5206\u6790\uff1a\u56e0\u4e3a\u6211\u6ca1\u6709\u8bbe\u7f6e\u670d\u52a1\u7aef\u7684\u5b57\u7b26\u96c6\uff0c\u56e0\u6b64\u9ed8\u8ba4\u7684\u5b57\u7b26\u96c6\u4f7f\u7528\u7684\u662flatin1\uff0c\u5bf9\u4e8elatin1\u4e00\u4e2a\u5b57\u7b26\u4ee3\u8868\u4e00\u4e2a\u5b57\u8282\uff0c\u56e0\u6b64\u8fd9\u5217\u7684key_len\u7684\u957f\u5ea6\u662f20\uff0c\u8868\u793a\u4f7f\u7528\u4e86name\u8fd9\u4e2a\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u7ed9test_kl\u8868\uff0c\u65b0\u589ename1\u5217\uff0c\u8be5\u5217\u6ca1\u6709\u8bbe\u7f6e\u201cnot null\u201d<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 676px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005517836.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2973372781065089\" data-type=\"png\" data-w=\"676\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 676px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005517836.png\" data-ratio=\"0.2973372781065089\" data-type=\"png\" data-w=\"676\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5206\u6790\uff1a\u5982\u679c\u7d22\u5f15\u5b57\u6bb5\u53ef\u4ee5\u4e3anull\uff0c\u5219mysql\u5e95\u5c42\u4f1a\u4f7f\u75281\u4e2a\u5b57\u8282\u7528\u4e8e\u6807\u8bc6\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 \u5220\u9664\u539f\u6765\u7684\u7d22\u5f15name\u548cname1\uff0c\u65b0\u589e\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664\u539f\u6765\u7684\u7d22\u5f15name\u548cname1<\/span>\ndrop\u00a0index\u00a0index_name\u00a0on\u00a0test_kl\u00a0;\ndrop\u00a0index\u00a0index_name1\u00a0on\u00a0test_kl\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u589e\u52a0\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0name_name1_index\u00a0on\u00a0test_kl(name,name1);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0test_kl\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0name1\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\u00a0--121\nexplain\u00a0select\u00a0*\u00a0from\u00a0test_kl\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0name\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\u00a0--60\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005518417.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.45322793148880103\" data-type=\"png\" data-w=\"759\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005518417.png\" data-ratio=\"0.45322793148880103\" data-type=\"png\" data-w=\"759\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u5bf9\u4e8e\u4e0b\u9762\u8fd9\u4e2a\u6267\u884c\u8ba1\u5212\uff0c\u53ef\u4ee5\u770b\u5230\u6211\u4eec\u53ea\u4f7f\u7528\u4e86\u590d\u5408\u7d22\u5f15\u7684\u7b2c\u4e00\u4e2a\u7d22\u5f15\u5b57\u6bb5name\uff0c\u56e0\u6b64key_len\u662f20\uff0c\u8fd9\u4e2a\u5f88\u6e05\u695a\u3002\u518d\u770b\u4e0a\u9762\u8fd9\u4e2a\u6267\u884c\u8ba1\u5212\uff0c\u6211\u4eec\u867d\u7136\u4ec5\u4ec5\u5728where\u540e\u9762\u4f7f\u7528\u4e86\u590d\u5408\u7d22\u5f15\u5b57\u6bb5\u4e2d\u7684name1\u5b57\u6bb5\uff0c\u4f46\u662f\u4f60\u8981\u4f7f\u7528\u590d\u5408\u7d22\u5f15\u7684\u7b2c2\u4e2a\u7d22\u5f15\u5b57\u6bb5\uff0c\u4f1a\u9ed8\u8ba4\u4f7f\u7528\u4e86\u590d\u5408\u7d22\u5f15\u7684\u7b2c1\u4e2a\u7d22\u5f15\u5b57\u6bb5name\uff0c\u7531\u4e8ename1\u53ef\u4ee5\u662fnull\uff0c\u56e0\u6b64key_len = 20 + 20 + 1 = 41\u5440\uff01<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 \u518d\u6b21\u600e\u52a0\u4e00\u4e2aname2\u5b57\u6bb5\uff0c\u5e76\u4e3a\u8be5\u5b57\u6bb5\u521b\u5efa\u4e00\u4e2a\u7d22\u5f15\u3002<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e0d\u540c\u7684\u662f\uff1a\u8be5\u5b57\u6bb5\u6570\u636e\u7c7b\u578b\u662fvarchar<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u65b0\u589e\u4e00\u4e2a\u5b57\u6bb5name2\uff0cname2\u53ef\u4ee5\u4e3anull<\/span>\nalter\u00a0table\u00a0test_kl\u00a0add\u00a0column\u00a0name2\u00a0varchar(20)\u00a0;\u00a0\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u7ed9name2\u5b57\u6bb5\uff0c\u8bbe\u7f6e\u4e3a\u7d22\u5f15\u5b57\u6bb5<\/span>\nalter\u00a0table\u00a0test_kl\u00a0add\u00a0index\u00a0name2_index(name2)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0test_kl\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0name2\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\u00a0\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005518256.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2503419972640219\" data-type=\"png\" data-w=\"731\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005518256.png\" data-ratio=\"0.2503419972640219\" data-type=\"png\" data-w=\"731\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> key_len = 20 + 1 + 2\uff0c\u8fd9\u4e2a20 + 1\u6211\u4eec\u77e5\u9053\uff0c\u8fd9\u4e2a2\u53c8\u4ee3\u8868\u4ec0\u4e48\u5462\uff1f\u539f\u6765varchar\u5c5e\u4e8e\u53ef\u53d8\u957f\u5ea6\uff0c\u5728mysql\u5e95\u5c42\u4e2d\uff0c\u75282\u4e2a\u5b57\u8282\u6807\u8bc6\u53ef\u53d8\u957f\u5ea6\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>6\uff09ref<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8fd9\u91cc\u7684ref\u7684\u4f5c\u7528\uff0c\u6307\u660e\u5f53\u524d\u8868\u6240\u53c2\u7167\u7684\u5b57\u6bb5\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6ce8\u610f\u4e0etype\u4e2d\u7684ref\u503c\u533a\u5206\u3002\u5728type\u4e2d\uff0cref\u53ea\u662ftype\u7c7b\u578b\u7684\u4e00\u79cd\u9009\u9879\u503c\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u7ed9course\u8868\u7684tid\u5b57\u6bb5\uff0c\u6dfb\u52a0\u4e00\u4e2a\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0tid_index\u00a0on\u00a0course(tid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0course\u00a0c,teacher\u00a0t\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.tid\u00a0=\u00a0t.tid\u00a0\u00a0\nand\u00a0t.tname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'tw'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005519357.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2546583850931677\" data-type=\"png\" data-w=\"805\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005519357.png\" data-ratio=\"0.2546583850931677\" data-type=\"png\" data-w=\"805\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u6709\u4e24\u4e2a\u7d22\u5f15\uff0cc\u8868\u7684c.tid\u5f15\u7528\u7684\u662ft\u8868\u7684tid\u5b57\u6bb5\uff0c\u56e0\u6b64\u53ef\u4ee5\u770b\u5230\u663e\u793a\u7ed3\u679c\u4e3a\u3010\u6570\u636e\u5e93\u540d.t.tid\u3011\uff0ct\u8868\u7684t.name\u5f15\u7528\u7684\u662f\u4e00\u4e2a\u5e38\u91cf\"tw\"\uff0c\u56e0\u6b64\u53ef\u4ee5\u770b\u5230\u7ed3\u679c\u663e\u793a\u4e3aconst\uff0c\u8868\u793a\u4e00\u4e2a\u5e38\u91cf\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>7\uff09rows(\u8fd9\u4e2a\u76ee\u524d\u8fd8\u662f\u6709\u70b9\u7591\u60d1)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u88ab\u7d22\u5f15\u4f18\u5316\u67e5\u8be2\u7684\u6570\u636e\u4e2a\u6570 (\u5b9e\u9645\u901a\u8fc7\u7d22\u5f15\u800c\u67e5\u8be2\u5230\u7684\u6570\u636e\u4e2a\u6570)<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\nfrom\u00a0course\u00a0c,teacher\u00a0t\u00a0\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.tid\u00a0=\u00a0t.tid\nand\u00a0t.tname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'tz'<\/span>\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005520170.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5542168674698795\" data-type=\"png\" data-w=\"830\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005520170.png\" data-ratio=\"0.5542168674698795\" data-type=\"png\" data-w=\"830\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>8\uff09extra<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8868\u793a\u5176\u4ed6\u7684\u4e00\u4e9b\u8bf4\u660e\uff0c\u4e5f\u5f88\u6709\u7528\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 using filesort\uff1a\u9488\u5bf9\u5355\u7d22\u5f15\u7684\u60c5\u51b5<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u51fa\u73b0\u4e86\u8fd9\u4e2a\u8bcd\uff0c\u8868\u793a\u4f60\u5f53\u524d\u7684SQL\u6027\u80fd\u6d88\u8017\u8f83\u5927\u3002\u8868\u793a\u8fdb\u884c\u4e86\u4e00\u6b21\u201c\u989d\u5916\u201d\u7684\u6392\u5e8f\u3002\u5e38\u89c1\u4e8eorder by\u8bed\u53e5\u4e2d\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2160 \u4ec0\u4e48\u662f\u201c\u989d\u5916\u201d\u7684\u6392\u5e8f\uff1f<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e3a\u4e86\u8bb2\u6e05\u695a\u8fd9\u4e2a\uff0c\u6211\u4eec\u9996\u5148\u8981\u77e5\u9053\u4ec0\u4e48\u662f\u6392\u5e8f\u3002\u6211\u4eec\u4e3a\u4e86\u7ed9\u67d0\u4e00\u4e2a\u5b57\u6bb5\u8fdb\u884c\u6392\u5e8f\u7684\u65f6\u5019\uff0c\u9996\u5148\u4f60\u5f97\u5148\u67e5\u8be2\u5230\u8fd9\u4e2a\u5b57\u6bb5\uff0c\u7136\u540e\u5728\u5c06\u8fd9\u4e2a\u5b57\u6bb5\u8fdb\u884c\u6392\u5e8f\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7d27\u63a5\u7740\uff0c\u6211\u4eec\u67e5\u770b\u5982\u4e0b\u4e24\u4e2aSQL\u8bed\u53e5\u7684\u6267\u884c\u8ba1\u5212\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u65b0\u5efa\u4e00\u5f20\u8868\uff0c\u5efa\u8868\u540c\u65f6\u521b\u5efa\u7d22\u5f15<\/span>\ncreate\u00a0table\u00a0test02\n(\u00a0\u00a0\u00a0\n\u00a0\u00a0a1\u00a0char(3),\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0a2\u00a0char(3),\u00a0\u00a0\u00a0\n\u00a0\u00a0a3\u00a0char(3),\u00a0\u00a0\u00a0\n\u00a0\u00a0index\u00a0idx_a1(a1),\u00a0\u00a0\n\u00a0\u00a0index\u00a0idx_a2(a2),\u00a0\u00a0\u00a0\n\u00a0\u00a0index\u00a0idx_a3(a3)\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1\u00a0=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0order\u00a0by\u00a0a1\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1\u00a0=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0order\u00a0by\u00a0a2\u00a0;\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005521698.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.29782359679266895\" data-type=\"png\" data-w=\"873\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005521698.png\" data-ratio=\"0.29782359679266895\" data-type=\"png\" data-w=\"873\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u5bf9\u4e8e\u7b2c\u4e00\u4e2a\u6267\u884c\u8ba1\u5212\uff0cwhere\u540e\u9762\u6211\u4eec\u5148\u67e5\u8be2\u4e86a1\u5b57\u6bb5\uff0c\u7136\u540e\u518d\u5229\u7528a1\u505a\u4e86\u4f9d\u6b21\u6392\u5e8f\uff0c\u8fd9\u4e2a\u5f88\u8f7b\u677e\u3002\u4f46\u662f\u5bf9\u4e8e\u7b2c\u4e8c\u4e2a\u6267\u884c\u8ba1\u5212\uff0cwhere\u540e\u9762\u6211\u4eec\u67e5\u8be2\u4e86a1\u5b57\u6bb5\uff0c\u7136\u800c\u5229\u7528\u7684\u5374\u662fa2\u5b57\u6bb5\u8fdb\u884c\u6392\u5e8f\uff0c\u6b64\u65f6myql\u5e95\u5c42\u4f1a\u8fdb\u884c\u4e00\u6b21\u67e5\u8be2\uff0c\u8fdb\u884c\u201c\u989d\u5916\u201d\u7684\u6392\u5e8f\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u603b\u7ed3\uff1a\u5bf9\u4e8e\u5355\u7d22\u5f15\uff0c\u5982\u679c\u6392\u5e8f\u548c\u67e5\u627e\u662f\u540c\u4e00\u4e2a\u5b57\u6bb5\uff0c\u5219\u4e0d\u4f1a\u51fa\u73b0using filesort\uff1b\u5982\u679c\u6392\u5e8f\u548c\u67e5\u627e\u4e0d\u662f\u540c\u4e00\u4e2a\u5b57\u6bb5\uff0c\u5219\u4f1a\u51fa\u73b0using filesort\uff1b\u56e0\u6b64where\u54ea\u4e9b\u5b57\u6bb5\uff0c\u5c31order by\u54ea\u4e9b\u4e9b\u5b57\u6bb5\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 using filesort\uff1a\u9488\u5bf9\u590d\u5408\u7d22\u5f15\u7684\u60c5\u51b5<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e0d\u80fd\u8de8\u5217(\u5b98\u65b9\u672f\u8bed\uff1a\u6700\u4f73\u5de6\u524d\u7f00)<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664test02\u7684\u7d22\u5f15<\/span>\ndrop\u00a0index\u00a0idx_a1\u00a0on\u00a0test02;\ndrop\u00a0index\u00a0idx_a2\u00a0on\u00a0test02;\ndrop\u00a0index\u00a0idx_a3\u00a0on\u00a0test02;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/span>\nalter\u00a0table\u00a0test02\u00a0add\u00a0index\u00a0idx_a1_a2_a3\u00a0(a1,a2,a3)\u00a0;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u4e0b\u9762SQL\u8bed\u53e5\u7684\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0order\u00a0by\u00a0a3\u00a0;\u00a0\u00a0--using\u00a0filesort\nexplain\u00a0select\u00a0*from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a2=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0order\u00a0by\u00a0a3\u00a0;\u00a0--using\u00a0filesort\nexplain\u00a0select\u00a0*from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0order\u00a0by\u00a0a2\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005522867.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5684931506849316\" data-type=\"png\" data-w=\"876\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005522867.png\" data-ratio=\"0.5684931506849316\" data-type=\"png\" data-w=\"876\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u590d\u5408\u7d22\u5f15\u7684\u987a\u5e8f\u662f(a1,a2,a3)\uff0c\u53ef\u4ee5\u770b\u5230a1\u5728\u6700\u5de6\u8fb9\uff0c\u56e0\u6b64a1\u5c31\u53eb\u505a\u201c\u6700\u4f73\u5de6\u524d\u7f00\u201d\uff0c\u5982\u679c\u8981\u4f7f\u7528\u540e\u9762\u7684\u7d22\u5f15\u5b57\u6bb5\uff0c\u5fc5\u987b\u5148\u4f7f\u7528\u5230\u8fd9\u4e2aa1\u5b57\u6bb5\u3002\u5bf9\u4e8eexplain1\uff0cwhere\u540e\u9762\u6211\u4eec\u4f7f\u7528a1\u5b57\u6bb5\uff0c\u4f46\u662f\u540e\u9762\u7684\u6392\u5e8f\u4f7f\u7528\u4e86a3\uff0c\u76f4\u63a5\u8df3\u8fc7\u4e86a2\uff0c\u5c5e\u4e8e\u8de8\u5217\uff1b\u5bf9\u4e8eexplain2\uff0cwhere\u540e\u9762\u6211\u4eec\u4f7f\u7528\u4e86a2\u5b57\u6bb5\uff0c\u76f4\u63a5\u8df3\u8fc7\u4e86a1\u5b57\u6bb5\uff0c\u4e5f\u5c5e\u4e8e\u8de8\u5217\uff1b\u5bf9\u4e8eexplain3\uff0cwhere\u540e\u9762\u6211\u4eec\u4f7f\u7528a1\u5b57\u6bb5\uff0c\u540e\u9762\u4f7f\u7528\u7684\u662fa2\u5b57\u6bb5\uff0c\u56e0\u6b64\u6ca1\u6709\u51fa\u73b0\u3010using filesort\u3011\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 using temporary<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u51fa\u73b0\u4e86\u8fd9\u4e2a\u8bcd\uff0c\u4e5f\u8868\u793a\u4f60\u5f53\u524d\u7684SQL\u6027\u80fd\u6d88\u8017\u8f83\u5927\u3002\u8fd9\u662f\u7531\u4e8e\u5f53\u524dSQL\u7528\u5230\u4e86\u4e34\u65f6\u8868\u3002\u4e00\u822c\u51fa\u73b0\u5728group by\u4e2d\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0a1\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>\u00a0(<span style=\"color: #98c379; line-height: 26px;\">'1'<\/span>,<span style=\"color: #98c379; line-height: 26px;\">'2'<\/span>,<span style=\"color: #98c379; line-height: 26px;\">'3'<\/span>)\u00a0group\u00a0by\u00a0a1\u00a0;\nexplain\u00a0select\u00a0a1\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>\u00a0(<span style=\"color: #98c379; line-height: 26px;\">'1'<\/span>,<span style=\"color: #98c379; line-height: 26px;\">'2'<\/span>,<span style=\"color: #98c379; line-height: 26px;\">'3'<\/span>)\u00a0group\u00a0by\u00a0a2\u00a0;\u00a0--using\u00a0temporary\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005524304.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.24743326488706366\" data-type=\"png\" data-w=\"974\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005524304.png\" data-ratio=\"0.24743326488706366\" data-type=\"png\" data-w=\"974\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u5f53\u4f60\u67e5\u8be2\u54ea\u4e2a\u5b57\u6bb5\uff0c\u5c31\u6309\u7167\u90a3\u4e2a\u5b57\u6bb5\u5206\u7ec4\uff0c\u5426\u5219\u5c31\u4f1a\u51fa\u73b0using temporary\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u9488\u5bf9using temporary\uff0c\u6211\u4eec\u5728\u770b\u4e00\u4e2a\u4f8b\u5b50\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">using temporary\u8868\u793a\u9700\u8981\u989d\u5916\u518d\u4f7f\u7528\u4e00\u5f20\u8868\uff0c\u4e00\u822c\u51fa\u73b0\u5728group by\u8bed\u53e5\u4e2d\u3002\u867d\u7136\u5df2\u7ecf\u6709\u8868\u4e86\uff0c\u4f46\u662f\u4e0d\u9002\u7528\uff0c\u5fc5\u987b\u518d\u6765\u4e00\u5f20\u8868\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u518d\u6b21\u6765\u770bmysql\u7684\u7f16\u5199\u8fc7\u7a0b\u548c\u89e3\u6790\u8fc7\u7a0b\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2160 \u7f16\u5199\u8fc7\u7a0b<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">select\u00a0dinstinct\u00a0\u00a0..from\u00a0\u00a0..join\u00a0..on\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0..group\u00a0by\u00a0..having\u00a0..order\u00a0by\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">limit<\/span>\u00a0..\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2161 \u89e3\u6790\u8fc7\u7a0b<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">from\u00a0..\u00a0on..\u00a0join\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0..group\u00a0by\u00a0..having\u00a0..select\u00a0dinstinct\u00a0..order\u00a0by\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">limit<\/span>\u00a0..\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f88\u663e\u7136\uff0cwhere\u540e\u662fgroup by\uff0c\u7136\u540e\u624d\u662fselect\u3002\u57fa\u4e8e\u6b64\uff0c\u6211\u4eec\u518d\u67e5\u770b\u5982\u4e0b\u4e24\u4e2aSQL\u8bed\u53e5\u7684\u6267\u884c\u8ba1\u5212\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0test03\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a2=2\u00a0and\u00a0a4=4\u00a0group\u00a0by\u00a0a2,a4;\nexplain\u00a0select\u00a0*\u00a0from\u00a0test03\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a2=2\u00a0and\u00a0a4=4\u00a0group\u00a0by\u00a0a3;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u5206\u6790\u5982\u4e0b\uff1a<\/strong> \u5bf9\u4e8e\u7b2c\u4e00\u4e2a\u6267\u884c\u8ba1\u5212\uff0cwhere\u540e\u9762\u662fa2\u548ca4\uff0c\u63a5\u7740\u6211\u4eec\u6309\u7167a2\u548ca4\u5206\u7ec4\uff0c\u5f88\u660e\u663e\u8fd9\u4e24\u5f20\u8868\u5df2\u7ecf\u6709\u4e86\uff0c\u76f4\u63a5\u5728a2\u548ca4\u4e0a\u5206\u7ec4\u5c31\u884c\u4e86\u3002\u4f46\u662f\u5bf9\u4e8e\u7b2c\u4e8c\u4e2a\u6267\u884c\u8ba1\u5212\uff0cwhere\u540e\u9762\u662fa2\u548ca4\uff0c\u63a5\u7740\u6211\u4eec\u5374\u6309\u7167a3\u5206\u7ec4\uff0c\u5f88\u660e\u663e\u6211\u4eec\u6ca1\u6709a3\u8fd9\u5f20\u8868\uff0c\u56e0\u6b64\u6709\u9700\u8981\u518d\u6765\u4e00\u5f20\u4e34\u65f6\u8868a3\u3002\u56e0\u6b64\u5c31\u4f1a\u51fa\u73b0using temporary\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 using index<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u4f60\u770b\u5230\u8fd9\u4e2a\u5173\u952e\u8bcd\uff0c\u606d\u559c\u4f60\uff0c\u8868\u793a\u4f60\u7684SQL\u6027\u80fd\u63d0\u5347\u4e86\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">using index\u79f0\u4e4b\u4e3a\u201c\u7d22\u5f15\u8986\u76d6\u201d\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u51fa\u73b0\u4e86using index\uff0c\u5c31\u8868\u793a\u4e0d\u7528\u8bfb\u53d6\u6e90\u8868\uff0c\u800c\u53ea\u5229\u7528\u7d22\u5f15\u83b7\u53d6\u6570\u636e\uff0c\u4e0d\u9700\u8981\u56de\u6e90\u8868\u67e5\u8be2\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u53ea\u8981\u4f7f\u7528\u5230\u7684\u5217\uff0c\u5168\u90e8\u51fa\u73b0\u5728\u7d22\u5f15\u4e2d\uff0c\u5c31\u662f\u7d22\u5f15\u8986\u76d6\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664test02\u4e2d\u7684\u590d\u5408\u7d22\u5f15idx_a1_a2_a3<\/span>\ndrop\u00a0index\u00a0idx_a1_a2_a3\u00a0on\u00a0test02;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u91cd\u65b0\u521b\u5efa\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/span>\nidx_a1_a2create\u00a0index\u00a0idx_a1_a2\u00a0on\u00a0test02(a1,a2);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a1,a3\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0or\u00a0a3=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\nexplain\u00a0select\u00a0a1,a2\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0and\u00a0a2=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005526915.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.36538461538461536\" data-type=\"png\" data-w=\"936\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005526915.png\" data-ratio=\"0.36538461538461536\" data-type=\"png\" data-w=\"936\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u6211\u4eec\u521b\u5efa\u7684\u662fa1\u548ca2\u7684\u590d\u5408\u7d22\u5f15\uff0c\u5bf9\u4e8e\u7b2c\u4e00\u4e2a\u6267\u884c\u8ba1\u5212\uff0c\u6211\u4eec\u5374\u51fa\u73b0\u4e86a3\uff0c\u8be5\u5b57\u6bb5\u5e76\u6ca1\u6709\u521b\u5efa\u7d22\u5f15\uff0c\u56e0\u6b64\u6ca1\u6709\u51fa\u73b0using index\uff0c\u800c\u662fusing where\uff0c\u8868\u793a\u6211\u4eec\u9700\u8981\u56de\u8868\u67e5\u8be2\u3002\u5bf9\u4e8e\u7b2c\u4e8c\u4e2a\u6267\u884c\u8ba1\u5212\uff0c\u5c5e\u4e8e\u5b8c\u5168\u7684\u7d22\u5f15\u8986\u76d6\uff0c\u56e0\u6b64\u51fa\u73b0\u4e86using index\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u9488\u5bf9using index\uff0c\u6211\u4eec\u5728\u67e5\u770b\u4e00\u4e2a\u6848\u4f8b\uff1a<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0a1,a2\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0or\u00a0a2=\u00a0<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0;\nexplain\u00a0select\u00a0a1,a2\u00a0from\u00a0test02;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5982\u679c\u7528\u5230\u4e86\u7d22\u5f15\u8986\u76d6(using index\u65f6)\uff0c\u4f1a\u5bf9possible_keys\u548ckey\u9020\u6210\u5f71\u54cd\uff1a<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">a.\u5982\u679c\u6ca1\u6709where\uff0c\u5219\u7d22\u5f15\u53ea\u51fa\u73b0\u5728key\u4e2d\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">b.\u5982\u679c\u6709where\uff0c\u5219\u7d22\u5f15 \u51fa\u73b0\u5728key\u548cpossible_keys\u4e2d\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2464 using where<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8868\u793a\u9700\u8981\u3010\u56de\u8868\u67e5\u8be2\u3011\uff0c\u8868\u793a\u65e2\u5728\u7d22\u5f15\u4e2d\u8fdb\u884c\u4e86\u67e5\u8be2\uff0c\u53c8\u56de\u5230\u4e86\u6e90\u8868\u8fdb\u884c\u4e86\u67e5\u8be2\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664test02\u4e2d\u7684\u590d\u5408\u7d22\u5f15idx_a1_a2<\/span>\ndrop\u00a0index\u00a0idx_a1_a2\u00a0on\u00a0test02;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5c06a1\u5b57\u6bb5\uff0c\u65b0\u589e\u4e3a\u4e00\u4e2a\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0a1_index\u00a0on\u00a0test02(a1);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a1,a3\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">\"\"<\/span>\u00a0and\u00a0a3=<span style=\"color: #98c379; line-height: 26px;\">\"\"<\/span>\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005527539.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.18435754189944134\" data-type=\"png\" data-w=\"895\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005527539.png\" data-ratio=\"0.18435754189944134\" data-type=\"png\" data-w=\"895\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u6211\u4eec\u65e2\u4f7f\u7528\u4e86\u7d22\u5f15a1\uff0c\u8868\u793a\u6211\u4eec\u4f7f\u7528\u4e86\u7d22\u5f15\u8fdb\u884c\u67e5\u8be2\u3002\u4f46\u662f\u53c8\u5bf9\u4e8ea3\u5b57\u6bb5\uff0c\u6211\u4eec\u5e76\u6ca1\u6709\u4f7f\u7528\u7d22\u5f15\uff0c\u56e0\u6b64\u5bf9\u4e8ea3\u5b57\u6bb5\uff0c\u9700\u8981\u56de\u6e90\u8868\u67e5\u8be2\uff0c\u8fd9\u4e2a\u65f6\u5019\u51fa\u73b0\u4e86using where\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2465 impossible where(\u4e86\u89e3)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53where\u5b50\u53e5\u6c38\u8fdc\u4e3aFalse\u7684\u65f6\u5019\uff0c\u4f1a\u51fa\u73b0impossible where<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a1\u00a0from\u00a0test02\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">\"a\"<\/span>\u00a0and\u00a0a1=<span style=\"color: #98c379; line-height: 26px;\">\"b\"<\/span>\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005528450.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.13903743315508021\" data-type=\"png\" data-w=\"935\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005528450.png\" data-ratio=\"0.13903743315508021\" data-type=\"png\" data-w=\"935\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>6\u3001\u4f18\u5316\u793a\u4f8b<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09\u5f15\u5165\u6848\u4f8b<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u65b0\u8868<\/span>\ncreate\u00a0table\u00a0test03\n(\u00a0\u00a0\n\u00a0\u00a0a1\u00a0int(4)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\n\u00a0\u00a0a2\u00a0int(4)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0a3\u00a0int(4)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\n\u00a0\u00a0a4\u00a0int(4)\u00a0not\u00a0null\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0a1_a2_a3_test03\u00a0on\u00a0test03(a1,a2,a3);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a3\u00a0from\u00a0test03\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=1\u00a0and\u00a0a2=2\u00a0and\u00a0a3=3;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005529264.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.36987951807228914\" data-type=\"png\" data-w=\"830\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005529264.png\" data-ratio=\"0.36987951807228914\" data-type=\"png\" data-w=\"830\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u63a8\u8350\u5199\u6cd5\uff1a<\/strong> \u590d\u5408\u7d22\u5f15\u987a\u5e8f\u548c\u4f7f\u7528\u987a\u5e8f\u4e00\u81f4\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4e0b\u9762\u770b\u770b\u3010<strong>\u4e0d\u63a8\u8350\u5199\u6cd5<\/strong>\u3011\uff1a\u590d\u5408\u7d22\u5f15\u987a\u5e8f\u548c\u4f7f\u7528\u987a\u5e8f\u4e0d\u4e00\u81f4\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a3\u00a0from\u00a0test03\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a3=1\u00a0and\u00a0a2=2\u00a0and\u00a0a1=3;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005530480.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.145933014354067\" data-type=\"png\" data-w=\"836\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005530480.png\" data-ratio=\"0.145933014354067\" data-type=\"png\" data-w=\"836\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u867d\u7136\u7ed3\u679c\u548c\u4e0a\u8ff0\u7ed3\u679c\u4e00\u81f4\uff0c\u4f46\u662f\u4e0d\u63a8\u8350\u8fd9\u6837\u5199\u3002\u4f46\u662f\u8fd9\u6837\u5199\u600e\u4e48\u53c8\u6ca1\u6709\u95ee\u9898\u5462\uff1f\u8fd9\u662f\u7531\u4e8eSQL\u4f18\u5316\u5668\u7684\u529f\u52b3\uff0c\u5b83\u5e2e\u6211\u4eec\u8c03\u6574\u4e86\u987a\u5e8f\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6700\u540e\u518d\u8865\u5145\u4e00\u70b9\uff1a\u5bf9\u4e8e\u590d\u5408\u7d22\u5f15\uff0c\u4e0d\u8981\u8de8\u5217\u4f7f\u7528<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0a3\u00a0from\u00a0test03\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0a1=1\u00a0and\u00a0a3=2\u00a0group\u00a0by\u00a0a3;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005531355.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.18241469816272965\" data-type=\"png\" data-w=\"762\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005531355.png\" data-ratio=\"0.18241469816272965\" data-type=\"png\" data-w=\"762\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> a1_a2_a3\u662f\u4e00\u4e2a\u590d\u5408\u7d22\u5f15\uff0c\u6211\u4eec\u4f7f\u7528a1\u7d22\u5f15\u540e\uff0c\u76f4\u63a5\u8de8\u5217\u4f7f\u7528\u4e86a3\uff0c\u76f4\u63a5\u8df3\u8fc7\u7d22\u5f15a2\uff0c\u56e0\u6b64\u7d22\u5f15a3\u5931\u6548\u4e86\uff0c\u5f53\u4f7f\u7528a3\u8fdb\u884c\u5206\u7ec4\u7684\u65f6\u5019\uff0c\u5c31\u4f1a\u51fa\u73b0using where\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09\u5355\u8868\u4f18\u5316<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u65b0\u8868<\/span>\ncreate\u00a0table\u00a0book\n(\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0bid\u00a0int(4)\u00a0primary\u00a0key,\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0name\u00a0varchar(20)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0authorid\u00a0int(4)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0publicid\u00a0int(4)\u00a0not\u00a0null,\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0typeid\u00a0int(4)\u00a0not\u00a0null\u00a0\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u63d2\u5165\u6570\u636e<\/span>\ninsert\u00a0into\u00a0book\u00a0values(1,<span style=\"color: #98c379; line-height: 26px;\">'tjava'<\/span>,1,1,2)\u00a0;\ninsert\u00a0into\u00a0book\u00a0values(2,<span style=\"color: #98c379; line-height: 26px;\">'tc'<\/span>,2,1,2)\u00a0;\ninsert\u00a0into\u00a0book\u00a0values(3,<span style=\"color: #98c379; line-height: 26px;\">'wx'<\/span>,3,2,1)\u00a0;\ninsert\u00a0into\u00a0book\u00a0values(4,<span style=\"color: #98c379; line-height: 26px;\">'math'<\/span>,4,2,3)\u00a0;\u00a0\u00a0\u00a0\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 355px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005532754.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.5098591549295775\" data-type=\"png\" data-w=\"355\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 355px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005532754.png\" data-ratio=\"0.5098591549295775\" data-type=\"png\" data-w=\"355\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6848\u4f8b\uff1a\u67e5\u8be2authorid=1\u4e14typeid\u4e3a2\u62163\u7684bid\uff0c\u5e76\u6839\u636etypeid\u964d\u5e8f\u6392\u5217\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0\nselect\u00a0bid\u00a0from\u00a0book\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0typeid\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>(2,3)\u00a0and\u00a0authorid=1\u00a0\norder\u00a0by\u00a0typeid\u00a0desc\u00a0;\u00a0\u00a0\u00a0\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005532790.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.21418826739427013\" data-type=\"png\" data-w=\"733\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005532790.png\" data-ratio=\"0.21418826739427013\" data-type=\"png\" data-w=\"733\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u8fd9\u662f\u6ca1\u6709\u8fdb\u884c\u4efb\u4f55\u4f18\u5316\u7684SQL\uff0c\u53ef\u4ee5\u770b\u5230typ\u4e3aALL\u7c7b\u578b\uff0cextra\u4e3ausing filesort\uff0c\u53ef\u4ee5\u60f3\u8c61\u8fd9\u4e2aSQL\u6709\u591a\u6050\u6016\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4f18\u5316\uff1a\u6dfb\u52a0\u7d22\u5f15\u7684\u65f6\u5019\uff0c\u8981\u6839\u636eMySQL\u89e3\u6790\u987a\u5e8f\u6dfb\u52a0\u7d22\u5f15\uff0c\u53c8\u56de\u5230\u4e86MySQL\u7684\u89e3\u6790\u987a\u5e8f\uff0c\u4e0b\u9762\u6211\u4eec\u518d\u6765\u770b\u770bMySQL\u7684\u89e3\u6790\u987a\u5e8f\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">from\u00a0..\u00a0on..\u00a0join\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0..group\u00a0by\u00a0..having\u00a0..select\u00a0dinstinct\u00a0..order\u00a0by\u00a0..<span style=\"color: #e6c07b; line-height: 26px;\">limit<\/span>\u00a0..\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u4f18\u53161\uff1a\u57fa\u4e8e\u6b64\uff0c\u6211\u4eec\u8fdb\u884c\u7d22\u5f15\u7684\u6dfb\u52a0\uff0c\u5e76\u518d\u6b21\u67e5\u770b\u6267\u884c\u8ba1\u5212\u3002<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u6dfb\u52a0\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0typeid_authorid_bid\u00a0on\u00a0book(typeid,authorid,bid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u518d\u6b21\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0\nselect\u00a0bid\u00a0from\u00a0book\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0typeid\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>(2,3)\u00a0and\u00a0authorid=1\u00a0\u00a0\norder\u00a0by\u00a0typeid\u00a0desc\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005533665.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2597864768683274\" data-type=\"png\" data-w=\"843\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005533665.png\" data-ratio=\"0.2597864768683274\" data-type=\"png\" data-w=\"843\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u7ed3\u679c\u5e76\u4e0d\u662f\u548c\u6211\u4eec\u60f3\u8c61\u7684\u4e00\u6837\uff0c\u8fd8\u662f\u51fa\u73b0\u4e86using where\uff0c\u67e5\u770b\u7d22\u5f15\u957f\u5ea6key_len=8\uff0c\u8868\u793a\u6211\u4eec\u53ea\u4f7f\u7528\u4e862\u4e2a\u7d22\u5f15\uff0c\u6709\u4e00\u4e2a\u7d22\u5f15\u5931\u6548\u4e86\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u4f18\u53162\uff1a\u4f7f\u7528\u4e86in\u6709\u65f6\u5019\u4f1a\u5bfc\u81f4\u7d22\u5f15\u5931\u6548\uff0c\u57fa\u4e8e\u6b64\u6709\u4e86\u5982\u4e0b\u4e00\u79cd\u4f18\u5316\u601d\u8def\u3002<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5c06in\u5b57\u6bb5\u653e\u5728\u6700\u540e\u9762\u3002\u9700\u8981\u6ce8\u610f\u4e00\u70b9\uff1a\u6bcf\u6b21\u521b\u5efa\u65b0\u7684\u7d22\u5f15\u7684\u65f6\u5019\uff0c\u6700\u597d\u662f\u5220\u9664\u4ee5\u524d\u7684\u5e9f\u5f03\u7d22\u5f15\uff0c\u5426\u5219\u6709\u65f6\u5019\u4f1a\u4ea7\u751f\u5e72\u6270(\u7d22\u5f15\u4e4b\u95f4)\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664\u4ee5\u524d\u7684\u7d22\u5f15<\/span>\ndrop\u00a0index\u00a0typeid_authorid_bid\u00a0on\u00a0book;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u518d\u6b21\u521b\u5efa\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0authorid_typeid_bid\u00a0on\u00a0book(authorid,typeid,bid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u518d\u6b21\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0\nselect\u00a0bid\u00a0from\u00a0book\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid=1\u00a0\u00a0and\u00a0typeid\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>(2,3)\u00a0\norder\u00a0by\u00a0typeid\u00a0desc\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005534107.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.09501187648456057\" data-type=\"png\" data-w=\"842\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005534107.png\" data-ratio=\"0.09501187648456057\" data-type=\"png\" data-w=\"842\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u8fd9\u91cc\u867d\u7136\u6ca1\u6709\u53d8\u5316\uff0c\u4f46\u662f\u8fd9\u662f\u4e00\u79cd\u4f18\u5316\u601d\u8def\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u603b\u7ed3\u5982\u4e0b\uff1a<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>a.\u6700\u4f73\u505a\u524d\u7f00\uff0c\u4fdd\u6301\u7d22\u5f15\u7684\u5b9a\u4e49\u548c\u4f7f\u7528\u7684\u987a\u5e8f\u4e00\u81f4\u6027<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>b.\u7d22\u5f15\u9700\u8981\u9010\u6b65\u4f18\u5316(\u6bcf\u6b21\u521b\u5efa\u65b0\u7d22\u5f15\uff0c\u6839\u636e\u60c5\u51b5\u9700\u8981\u5220\u9664\u4ee5\u524d\u7684\u5e9f\u5f03\u7d22\u5f15)<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>c.\u5c06\u542bIn\u7684\u8303\u56f4\u67e5\u8be2\uff0c\u653e\u5230where\u6761\u4ef6\u7684\u6700\u540e\uff0c\u9632\u6b62\u5931\u6548\u3002<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u672c\u4f8b\u4e2d\u540c\u65f6\u51fa\u73b0\u4e86Using where\uff08\u9700\u8981\u56de\u539f\u8868\uff09; Using index\uff08\u4e0d\u9700\u8981\u56de\u539f\u8868\uff09\uff1a\u539f\u56e0\uff0cwhere authorid=1 and typeid in(2,3)\u4e2dauthorid\u5728\u7d22\u5f15(authorid,typeid,bid)\u4e2d\uff0c\u56e0\u6b64\u4e0d\u9700\u8981\u56de\u539f\u8868\uff08\u76f4\u63a5\u5728\u7d22\u5f15\u8868\u4e2d\u80fd\u67e5\u5230\uff09\uff1b\u800ctypeid\u867d\u7136\u4e5f\u5728\u7d22\u5f15(authorid,typeid,bid)\u4e2d\uff0c\u4f46\u662f\u542bin\u7684\u8303\u56f4\u67e5\u8be2\u5df2\u7ecf\u4f7f\u8be5typeid\u7d22\u5f15\u5931\u6548\uff0c\u56e0\u6b64\u76f8\u5f53\u4e8e\u6ca1\u6709typeid\u8fd9\u4e2a\u7d22\u5f15\uff0c\u6240\u4ee5\u9700\u8981\u56de\u539f\u8868\uff08using where\uff09\uff1b<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u4f8b\u5982\u4ee5\u4e0b\u6ca1\u6709\u4e86In\uff0c\u5219\u4e0d\u4f1a\u51fa\u73b0using where\uff1a<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0bid\u00a0from\u00a0book\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0\u00a0authorid=1\u00a0and\u00a0typeid\u00a0=3\norder\u00a0by\u00a0typeid\u00a0desc\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005535209.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.20580474934036938\" data-type=\"png\" data-w=\"758\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005535209.png\" data-ratio=\"0.20580474934036938\" data-type=\"png\" data-w=\"758\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>3\uff09\u4e24\u8868\u4f18\u5316<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efateacher2\u65b0\u8868<\/span>\ncreate\u00a0table\u00a0teacher2\n(\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0tid\u00a0int(4)\u00a0primary\u00a0key,\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0cid\u00a0int(4)\u00a0not\u00a0null\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u63d2\u5165\u6570\u636e<\/span>\ninsert\u00a0into\u00a0teacher2\u00a0values(1,2);\ninsert\u00a0into\u00a0teacher2\u00a0values(2,1);\ninsert\u00a0into\u00a0teacher2\u00a0values(3,3);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efacourse2\u65b0\u8868<\/span>\ncreate\u00a0table\u00a0course2\n(\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0cid\u00a0int(4)\u00a0,\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0cname\u00a0varchar(20)\n);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u63d2\u5165\u6570\u636e<\/span>\ninsert\u00a0into\u00a0course2\u00a0values(1,<span style=\"color: #98c379; line-height: 26px;\">'java'<\/span>);\ninsert\u00a0into\u00a0course2\u00a0values(2,<span style=\"color: #98c379; line-height: 26px;\">'python'<\/span>);\ninsert\u00a0into\u00a0course2\u00a0values(3,<span style=\"color: #98c379; line-height: 26px;\">'kotlin'<\/span>);\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u6848\u4f8b\uff1a\u4f7f\u7528\u4e00\u4e2a\u5de6\u8fde\u63a5\uff0c\u67e5\u627e\u6559java\u8bfe\u7a0b\u7684\u6240\u6709\u4fe1\u606f\u3002<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0\nselect\u00a0*\nfrom\u00a0teacher2\u00a0t\nleft\u00a0outer\u00a0join\u00a0course2\u00a0c\non\u00a0t.cid=c.cid\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.cname=<span style=\"color: #98c379; line-height: 26px;\">'java'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005535777.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.25635103926096997\" data-type=\"png\" data-w=\"866\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005535777.png\" data-ratio=\"0.25635103926096997\" data-type=\"png\" data-w=\"866\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u4f18\u5316<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5bf9\u4e8e\u4e24\u5f20\u8868\uff0c\u7d22\u5f15\u5f80\u54ea\u91cc\u52a0\uff1f\u7b54\uff1a\u5bf9\u4e8e\u8868\u8fde\u63a5\uff0c\u5c0f\u8868\u9a71\u52a8\u5927\u8868\u3002\u7d22\u5f15\u5efa\u7acb\u5728\u7ecf\u5e38\u4f7f\u7528\u7684\u5b57\u6bb5\u4e0a\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u4e3a\u4ec0\u4e48\u5c0f\u8868\u9a71\u52a8\u5927\u8868\u597d\u4e00\u4e9b\u5462\uff1f<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">\u00a0\u00a0\u00a0\u00a0\u5c0f\u8868:10\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0\u5927\u8868:300\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5c0f\u8868\u9a71\u52a8\u5927\u8868<\/span>\nselect\u00a0...<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0\u5c0f\u8868.x10=\u5927\u8868.x300\u00a0;\n<span style=\"color: #c678dd; line-height: 26px;\">for<\/span>(int\u00a0i=0;i&lt;\u5c0f\u8868.length10;i++)\n{\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0<span style=\"color: #c678dd; line-height: 26px;\">for<\/span>(int\u00a0j=0;j&lt;\u5927\u8868.length300;j++)\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0{\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0...\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0}\n}\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5927\u8868\u9a71\u52a8\u5c0f\u8868<\/span>\nselect\u00a0...<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0\u5927\u8868.x300=\u5c0f\u8868.x10\u00a0;\n<span style=\"color: #c678dd; line-height: 26px;\">for<\/span>(int\u00a0i=0;i&lt;\u5927\u8868.length300;i++)\n{\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0<span style=\"color: #c678dd; line-height: 26px;\">for<\/span>(int\u00a0j=0;j&lt;\u5c0f\u8868.length10;j++)\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0{\u00a0\u00a0\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0...\u00a0\u00a0\u00a0\n\u00a0\u00a0\u00a0\u00a0}\n}\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u5206\u6790\uff1a<\/strong> \u4ee5\u4e0a2\u4e2aFOR\u5faa\u73af\uff0c\u6700\u7ec8\u90fd\u4f1a\u5faa\u73af3000\u6b21\uff1b\u4f46\u662f\u5bf9\u4e8e\u53cc\u5c42\u5faa\u73af\u6765\u8bf4\uff1a\u4e00\u822c\u5efa\u8bae\uff0c\u5c06\u6570\u636e\u5c0f\u7684\u5faa\u73af\uff0c\u653e\u5916\u5c42\u3002\u6570\u636e\u5927\u7684\u5faa\u73af\uff0c\u653e\u5185\u5c42\u3002\u4e0d\u7528\u7ba1\u8fd9\u662f\u4e3a\u4ec0\u4e48\uff0c\u8fd9\u662f\u7f16\u7a0b\u8bed\u8a00\u7684\u4e00\u4e2a\u539f\u5219\uff0c\u5bf9\u4e8e\u53cc\u91cd\u5faa\u73af\uff0c\u5916\u5c42\u5faa\u73af\u5c11\uff0c\u5185\u5b58\u5faa\u73af\u5927\uff0c\u7a0b\u5e8f\u7684\u6027\u80fd\u8d8a\u9ad8\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u8bba\uff1a\u5f53\u7f16\u5199\u3010\u2026on t.cid=c.cid\u3011\u65f6\uff0c\u5c06\u6570\u636e\u91cf\u5c0f\u7684\u8868\u653e\u5de6\u8fb9\uff08\u5047\u8bbe\u6b64\u65f6t\u8868\u6570\u636e\u91cf\u5c0f\uff0cc\u8868\u6570\u636e\u91cf\u5927\u3002\uff09<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6211\u4eec\u5df2\u7ecf\u77e5\u9053\u4e86\uff0c\u5bf9\u4e8e\u4e24\u8868\u8fde\u63a5\uff0c\u9700\u8981\u5229\u7528\u5c0f\u8868\u9a71\u52a8\u5927\u8868\uff0c\u4f8b\u5982\u3010\u2026on t.cid=c.cid\u3011\uff0ct\u5982\u679c\u662f\u5c0f\u8868(10\u6761)\uff0cc\u5982\u679c\u662f\u5927\u8868(300\u6761)\uff0c\u90a3\u4e48t\u6bcf\u5faa\u73af1\u6b21\uff0c\u5c31\u9700\u8981\u5faa\u73af300\u6b21\uff0c\u5373t\u8868\u7684t.cid\u5b57\u6bb5\u5c5e\u4e8e\uff0c\u7ecf\u5e38\u4f7f\u7528\u7684\u5b57\u6bb5\uff0c\u56e0\u6b64\u9700\u8981\u7ed9cid\u5b57\u6bb5\u6dfb\u52a0\u7d22\u5f15\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u66f4\u6df1\u5165\u7684\u8bf4\u660e\uff1a<\/strong> \u4e00\u822c\u60c5\u51b5\u4e0b\uff0c\u5de6\u8fde\u63a5\u7ed9\u5de6\u8868\u52a0\u7d22\u5f15\u3002\u53f3\u8fde\u63a5\u7ed9\u53f3\u8868\u52a0\u7d22\u5f15\u3002\u5176\u4ed6\u8868\u9700\u4e0d\u9700\u8981\u52a0\u7d22\u5f15\uff0c\u6211\u4eec\u9010\u6b65\u5c1d\u8bd5\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u7ed9\u5de6\u8868\u7684\u5b57\u6bb5\u52a0\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0cid_teacher2\u00a0on\u00a0teacher2(cid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0\nselect\u00a0*\nfrom\u00a0teacher2\u00a0t\u00a0\nleft\u00a0outer\u00a0join\u00a0course2\u00a0c\non\u00a0t.cid=c.cid\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.cname=<span style=\"color: #98c379; line-height: 26px;\">'java'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005536121.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.12757731958762886\" data-type=\"png\" data-w=\"776\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005536121.png\" data-ratio=\"0.12757731958762886\" data-type=\"png\" data-w=\"776\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u7136\u4f60\u53ef\u4ee5\u4e0b\u53bb\u63a5\u7740\u4f18\u5316\uff0c\u7ed9cname\u6dfb\u52a0\u4e00\u4e2a\u7d22\u5f15\u3002\u7d22\u5f15\u4f18\u5316\u662f\u4e00\u4e2a\u9010\u6b65\u7684\u8fc7\u7a0b\uff0c\u9700\u8981\u4e00\u70b9\u70b9\u5c1d\u8bd5\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u7ed9cname\u7684\u5b57\u6bb5\u52a0\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0cname_course2\u00a0on\u00a0course2(cname);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\nselect\u00a0t.cid,c.cname\nfrom\u00a0teacher2\u00a0t\nleft\u00a0outer\u00a0join\u00a0course2\u00a0c\non\u00a0t.cid=c.cid\u00a0\n<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0c.cname=<span style=\"color: #98c379; line-height: 26px;\">'java'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005537815.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.11086474501108648\" data-type=\"png\" data-w=\"902\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005537815.png\" data-ratio=\"0.11086474501108648\" data-type=\"png\" data-w=\"902\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6700\u540e\u8865\u5145\u4e00\u4e2a\uff1aUsing join buffer\u662fextra\u4e2d\u7684\u4e00\u4e2a\u9009\u9879\uff0c\u8868\u793aMysql\u5f15\u64ce\u4f7f\u7528\u4e86\u201c\u8fde\u63a5\u7f13\u5b58\u201d\uff0c\u5373MySQL\u5e95\u5c42\u52a8\u4e86\u4f60\u7684SQL\uff0c\u4f60\u5199\u7684\u592a\u5dee\u4e86\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>4\uff09\u4e09\u8868\u4f18\u5316<\/strong><\/p>\n<ul class=\"list-paddingleft-1\" style=\"margin-top: 8px; margin-bottom: 8px; padding-left: 25px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u5927\u4e8e\u7b49\u4e8e\u5f20\u8868\uff0c\u4f18\u5316\u539f\u5219\u4e00\u6837<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u5c0f\u8868\u9a71\u52a8\u5927\u8868<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u7d22\u5f15\u5efa\u7acb\u5728\u7ecf\u5e38\u67e5\u8be2\u7684\u5b57\u6bb5\u4e0a<\/section>\n<\/li>\n<\/ul>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>7\u3001\u907f\u514d\u7d22\u5f15\u5931\u6548\u7684\u4e00\u4e9b\u539f\u5219<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u590d\u5408\u7d22\u5f15\u9700\u8981\u6ce8\u610f\u7684\u70b9<\/strong><\/p>\n<ul class=\"list-paddingleft-1\" style=\"margin-top: 8px; margin-bottom: 8px; padding-left: 25px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u590d\u5408\u7d22\u5f15\uff0c\u4e0d\u8981\u8de8\u5217\u6216\u65e0\u5e8f\u4f7f\u7528(\u6700\u4f73\u5de6\u524d\u7f00)<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u590d\u5408\u7d22\u5f15\uff0c\u5c3d\u91cf\u4f7f\u7528\u5168\u7d22\u5f15\u5339\u914d\uff0c\u4e5f\u5c31\u662f\u8bf4\uff0c\u4f60\u5efa\u7acb\u51e0\u4e2a\u7d22\u5f15\uff0c\u5c31\u4f7f\u7528\u51e0\u4e2a\u7d22\u5f15<\/section>\n<\/li>\n<\/ul>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2461 \u4e0d\u8981\u5728\u7d22\u5f15\u4e0a\u8fdb\u884c\u4efb\u4f55\u64cd\u4f5c(\u8ba1\u7b97\u3001\u51fd\u6570\u3001\u7c7b\u578b\u8f6c\u6362)\uff0c\u5426\u5219\u7d22\u5f15\u5931\u6548<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0=\u00a01\u00a0and\u00a0typeid\u00a0=\u00a02;\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid*2\u00a0=\u00a01\u00a0and\u00a0typeid\u00a0=\u00a02\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<p style=\"outline: 0px;\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005538925.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2944038929440389\" data-type=\"png\" data-w=\"822\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005538925.png\" data-ratio=\"0.2944038929440389\" data-type=\"png\" data-w=\"822\" \/><\/noscript><\/p>\n<\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2462 \u7d22\u5f15\u4e0d\u80fd\u4f7f\u7528\u4e0d\u7b49\u4e8e\uff08!= &lt;&gt;\uff09\u6216is null (is not null)\uff0c\u5426\u5219\u81ea\u8eab\u4ee5\u53ca\u53f3\u4fa7\u6240\u6709\u5168\u90e8\u5931\u6548(\u9488\u5bf9\u5927\u591a\u6570\u60c5\u51b5)\u3002\u590d\u5408\u7d22\u5f15\u4e2d\u5982\u679c\u6709&gt;\uff0c\u5219\u81ea\u8eab\u548c\u53f3\u4fa7\u7d22\u5f15\u5168\u90e8\u5931\u6548\u3002<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u9488\u5bf9\u4e0d\u662f\u590d\u5408\u7d22\u5f15\u7684\u60c5\u51b5<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0!=\u00a01\u00a0and\u00a0typeid\u00a0=2\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0!=\u00a01\u00a0and\u00a0typeid\u00a0!=2\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005539155.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.39740820734341253\" data-type=\"png\" data-w=\"926\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005539155.png\" data-ratio=\"0.39740820734341253\" data-type=\"png\" data-w=\"926\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u518d\u89c2\u770b\u4e0b\u9762\u8fd9\u4e2a\u6848\u4f8b\uff1a<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664\u5355\u72ec\u7684\u7d22\u5f15<\/span>\ndrop\u00a0index\u00a0authorid_index\u00a0on\u00a0book;\ndrop\u00a0index\u00a0typeid_index\u00a0on\u00a0book;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u521b\u5efa\u4e00\u4e2a\u590d\u5408\u7d22\u5f15<\/span>\nalter\u00a0table\u00a0book\u00a0add\u00a0index\u00a0idx_book_at\u00a0(authorid,typeid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0&gt;\u00a01\u00a0and\u00a0typeid\u00a0=\u00a02\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0=\u00a01\u00a0and\u00a0typeid\u00a0&gt;\u00a02\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005540268.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.27682403433476394\" data-type=\"png\" data-w=\"932\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005540268.png\" data-ratio=\"0.27682403433476394\" data-type=\"png\" data-w=\"932\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u8bba\uff1a\u590d\u5408\u7d22\u5f15\u4e2d\u5982\u679c\u6709\u3010&gt;\u3011\uff0c\u5219\u81ea\u8eab\u548c\u53f3\u4fa7\u7d22\u5f15\u5168\u90e8\u5931\u6548\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5728\u770b\u770b\u590d\u5408\u7d22\u5f15\u4e2d\u6709\u3010&lt;\u3011\u7684\u60c5\u51b5\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005541870.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2926829268292683\" data-type=\"png\" data-w=\"902\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"margin-right: auto; margin-bottom: 8px; margin-left: auto; outline: 0px; box-sizing: border-box; font-family: -apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; background-color: #ffffff; cursor: zoom-in; display: block; border-radius: 4px; width: 677px !important; visibility: visible !important; height: auto !important; border: 0px initial initial;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005541870.png\" data-ratio=\"0.2926829268292683\" data-type=\"png\" data-w=\"902\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u6211\u4eec\u5b66\u4e60\u7d22\u5f15\u4f18\u5316 \uff0c\u662f\u4e00\u4e2a\u5927\u90e8\u5206\u60c5\u51b5\u9002\u7528\u7684\u7ed3\u8bba\uff0c\u4f46\u7531\u4e8eSQL\u4f18\u5316\u5668\u7b49\u539f\u56e0 \u8be5\u7ed3\u8bba\u4e0d\u662f100%\u6b63\u786e\u3002\u4e00\u822c\u800c\u8a00\uff0c \u8303\u56f4\u67e5\u8be2\uff08&gt; &lt; in\uff09\uff0c\u4e4b\u540e\u7684\u7d22\u5f15\u5931\u6548\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2463 SQL\u4f18\u5316\uff0c\u662f\u4e00\u79cd\u6982\u7387\u5c42\u9762\u7684\u4f18\u5316\u3002\u81f3\u4e8e\u662f\u5426\u5b9e\u9645\u4f7f\u7528\u4e86\u6211\u4eec\u7684\u4f18\u5316\uff0c\u9700\u8981\u901a\u8fc7explain\u8fdb\u884c\u63a8\u6d4b\u3002<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u5220\u9664\u590d\u5408\u7d22\u5f15<\/span>\ndrop\u00a0index\u00a0authorid_typeid_bid\u00a0on\u00a0book;\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u4e3aauthorid\u548ctypeid\uff0c\u5206\u522b\u521b\u5efa\u7d22\u5f15<\/span>\ncreate\u00a0index\u00a0authorid_index\u00a0on\u00a0book(authorid);\ncreate\u00a0index\u00a0typeid_index\u00a0on\u00a0book(typeid);\n<span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0=\u00a01\u00a0and\u00a0typeid\u00a0=2\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005542957.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.14161490683229813\" data-type=\"png\" data-w=\"805\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005542957.png\" data-ratio=\"0.14161490683229813\" data-type=\"png\" data-w=\"805\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u679c\u5206\u6790\uff1a<\/strong> \u6211\u4eec\u521b\u5efa\u4e86\u4e24\u4e2a\u7d22\u5f15\uff0c\u4f46\u662f\u5b9e\u9645\u4e0a\u53ea\u4f7f\u7528\u4e86\u4e00\u4e2a\u7d22\u5f15\u3002\u56e0\u4e3a\u5bf9\u4e8e\u4e24\u4e2a\u5355\u72ec\u7684\u7d22\u5f15\uff0c\u7a0b\u5e8f\u89c9\u5f97\u53ea\u7528\u4e00\u4e2a\u7d22\u5f15\u5c31\u591f\u4e86\uff0c\u4e0d\u9700\u8981\u4f7f\u7528\u4e24\u4e2a\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5f53\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u590d\u5408\u7d22\u5f15\uff0c\u518d\u6b21\u6267\u884c\u4e0a\u9762\u7684SQL\uff1a<\/p>\n<section style=\"padding-right: 10px; padding-left: 10px; line-height: 1.6; letter-spacing: 0px; word-break: break-word;\" data-tool=\"mdnice\u7f16\u8f91\u5668\" data-website=\"https:\/\/www.mdnice.com\">\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u67e5\u770b\u6267\u884c\u8ba1\u5212<\/span>\nexplain\u00a0select\u00a0*\u00a0from\u00a0book\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0authorid\u00a0=\u00a01\u00a0and\u00a0typeid\u00a0=2\u00a0;<\/code><\/pre>\n<\/section>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005543495.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.08916478555304741\" data-type=\"png\" data-w=\"886\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005543495.png\" data-ratio=\"0.08916478555304741\" data-type=\"png\" data-w=\"886\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2464 \u7d22\u5f15\u8986\u76d6\uff0c\u767e\u5206\u4e4b\u767e\u6ca1\u95ee\u9898<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2465 like\u5c3d\u91cf\u4ee5\u201c\u5e38\u91cf\u201d\u5f00\u5934\uff0c\u4e0d\u8981\u4ee5\u2019%'\u5f00\u5934\uff0c\u5426\u5219\u7d22\u5f15\u5931\u6548<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0like\u00a0<span style=\"color: #98c379; line-height: 26px;\">\"%x%\"<\/span>\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0like\u00a0<span style=\"color: #98c379; line-height: 26px;\">'x%'<\/span>;\nexplain\u00a0select\u00a0tname\u00a0from\u00a0teacher\u00a0\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0like\u00a0<span style=\"color: #98c379; line-height: 26px;\">'%x%'<\/span>;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005544830.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.41430192962542567\" data-type=\"png\" data-w=\"881\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005544830.png\" data-ratio=\"0.41430192962542567\" data-type=\"png\" data-w=\"881\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u7ed3\u8bba\u5982\u4e0b\uff1a<\/strong> like\u5c3d\u91cf\u4e0d\u8981\u4f7f\u7528\u7c7b\u4f3c\"%x%\"\u60c5\u51b5\uff0c\u4f46\u662f\u53ef\u4ee5\u4f7f\u7528\"x%\"\u60c5\u51b5\u3002\u5982\u679c\u975e\u4f7f\u7528 \"%x%\"\u60c5\u51b5\uff0c\u9700\u8981\u4f7f\u7528\u7d22\u5f15\u8986\u76d6\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2466 \u5c3d\u91cf\u4e0d\u8981\u4f7f\u7528\u7c7b\u578b\u8f6c\u6362\uff08\u663e\u793a\u3001\u9690\u5f0f\uff09\uff0c\u5426\u5219\u7d22\u5f15\u5931\u6548<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0=\u00a0<span style=\"color: #98c379; line-height: 26px;\">'abc'<\/span>\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0=\u00a0123\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005545590.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.2997512437810945\" data-type=\"png\" data-w=\"804\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005545590.png\" data-ratio=\"0.2997512437810945\" data-type=\"png\" data-w=\"804\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2467 \u5c3d\u91cf\u4e0d\u8981\u4f7f\u7528or\uff0c\u5426\u5219\u7d22\u5f15\u5931\u6548<\/strong><\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">explain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0and\u00a0tcid\u00a0&gt;1\u00a0;\nexplain\u00a0select\u00a0*\u00a0from\u00a0teacher\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0tname\u00a0=<span style=\"color: #98c379; line-height: 26px;\">''<\/span>\u00a0or\u00a0tcid\u00a0&gt;1\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<figure style=\"margin-top: 10px; margin-bottom: 10px; display: flex; flex-direction: column; justify-content: center; align-items: center;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><img decoding=\"async\" class=\"rich_pages wxw-img lazyload\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" data-src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005546882.png\" src=\"https:\/\/s.nmxc.ltd\/sakurairo_vision\/@2.6\/load_svg\/inload.svg\" onerror=\"imgError(this)\" data-ratio=\"0.27303370786516856\" data-type=\"png\" data-w=\"890\" \/><noscript><img decoding=\"async\" class=\"rich_pages wxw-img\" style=\"display: block; margin-right: auto; margin-left: auto; height: auto !important;\" src=\"https:\/\/wp-moto-1258805347.cos.ap-shanghai.myqcloud.com\/2023\/05\/20230528005546882.png\" data-ratio=\"0.27303370786516856\" data-type=\"png\" data-w=\"890\" \/><\/noscript><\/figure>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u6ce8\u610f\uff1aor\u5f88\u731b\uff0c\u4f1a\u8ba9\u81ea\u8eab\u7d22\u5f15\u548c\u5de6\u53f3\u4e24\u4fa7\u7684\u7d22\u5f15\u90fd\u5931\u6548\u3002<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>8\u3001\u4e00\u4e9b\u5176\u4ed6\u7684\u4f18\u5316\u65b9\u6cd5<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>1\uff09exists\u548cin\u7684\u4f18\u5316<\/strong><\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5982\u679c\u4e3b\u67e5\u8be2\u7684\u6570\u636e\u96c6\u5927\uff0c\u5219\u4f7f\u7528i\u5173\u952e\u5b57\uff0c\u6548\u7387\u9ad8\u3002<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5982\u679c\u5b50\u67e5\u8be2\u7684\u6570\u636e\u96c6\u5927\uff0c\u5219\u4f7f\u7528exist\u5173\u952e\u5b57,\u6548\u7387\u9ad8\u3002<\/p>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\">select\u00a0..from\u00a0table\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0exist\u00a0(\u5b50\u67e5\u8be2)\u00a0;\nselect\u00a0..from\u00a0table\u00a0<span style=\"color: #e6c07b; line-height: 26px;\">where<\/span>\u00a0\u5b57\u6bb5\u00a0<span style=\"color: #c678dd; line-height: 26px;\">in<\/span>\u00a0\u00a0(\u5b50\u67e5\u8be2)\u00a0;\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>2\uff09order by\u4f18\u5316<\/strong><\/p>\n<ul class=\"list-paddingleft-1\" style=\"margin-top: 8px; margin-bottom: 8px; padding-left: 25px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">IO\u5c31\u662f\u8bbf\u95ee\u786c\u76d8\u6587\u4ef6\u7684\u6b21\u6570<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">using filesort \u6709\u4e24\u79cd\u7b97\u6cd5\uff1a\u53cc\u8def\u6392\u5e8f\u3001\u5355\u8def\u6392\u5e8f\uff08\u6839\u636eIO\u7684\u6b21\u6570\uff09<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">MySQL4.1\u4e4b\u524d\u9ed8\u8ba4\u4f7f\u7528\u53cc\u8def\u6392\u5e8f\uff1b\u53cc\u8def\uff1a\u626b\u63cf2\u6b21\u78c1\u76d8(1\uff1a\u4ece\u78c1\u76d8\u8bfb\u53d6\u6392\u5e8f\u5b57\u6bb5,\u5bf9\u6392\u5e8f\u5b57\u6bb5\u8fdb\u884c\u6392\u5e8f(\u5728buffer\u4e2d\u8fdb\u884c\u7684\u6392\u5e8f)2\uff1a\u626b\u63cf\u5176\u4ed6\u5b57\u6bb5)<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">MySQL4.1\u4e4b\u540e\u9ed8\u8ba4\u4f7f\u7528\u5355\u8def\u6392\u5e8f\uff1a\u53ea\u8bfb\u53d6\u4e00\u6b21\uff08\u5168\u90e8\u5b57\u6bb5\uff09\uff0c\u5728buffer\u4e2d\u8fdb\u884c\u6392\u5e8f\u3002\u4f46\u79cd\u5355\u8def\u6392\u5e8f\u4f1a\u6709\u4e00\u5b9a\u7684\u9690\u60a3(\u4e0d\u4e00\u5b9a\u771f\u7684\u662f\u201c\u5355\u8def\/1\u6b21IO\u201d\uff0c\u6709\u53ef\u80fd\u591a\u6b21IO)\u3002\u539f\u56e0\uff1a\u5982\u679c\u6570\u636e\u91cf\u7279\u522b\u5927\uff0c\u5219\u65e0\u6cd5\u5c06\u6240\u6709\u5b57\u6bb5\u7684\u6570\u636e\u4e00\u6b21\u6027\u8bfb\u53d6\u5b8c\u6bd5\uff0c\u56e0\u6b64\u4f1a\u8fdb\u884c\u201c\u5206\u7247\u8bfb\u53d6\u3001\u591a\u6b21\u8bfb\u53d6\u201d\u3002<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u6ce8\u610f\uff1a\u5355\u8def\u6392\u5e8f \u6bd4\u53cc\u8def\u6392\u5e8f \u4f1a\u5360\u7528\u66f4\u591a\u7684buffer\u3002<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u5355\u8def\u6392\u5e8f\u5728\u4f7f\u7528\u65f6\uff0c\u5982\u679c\u6570\u636e\u5927\uff0c\u53ef\u4ee5\u8003\u8651\u8c03\u5927buffer\u7684\u5bb9\u91cf\u5927\u5c0f\uff1a<\/section>\n<\/li>\n<\/ul>\n<pre style=\"margin-top: 10px; margin-bottom: 10px; border-radius: 5px; box-shadow: rgba(0, 0, 0, 0.55) 0px 2px 10px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><code style=\"overflow-x: auto; padding: 16px; color: #abb2bf; display: -webkit-box; font-family: Operator Mono, Consolas, Monaco, Menlo, monospace; font-size: 12px; -webkit-overflow-scrolling: touch; padding-top: 15px; background: #282c34; border-radius: 5px;\"><span style=\"color: #5c6370; font-style: italic; line-height: 26px;\">#\u00a0\u4e0d\u4e00\u5b9a\u771f\u7684\u662f\u201c\u5355\u8def\/1\u6b21IO\u201d\uff0c\u6709\u53ef\u80fd\u591a\u6b21IO<\/span>\n<span style=\"color: #e6c07b; line-height: 26px;\">set<\/span>\u00a0max_length_for_sort_data\u00a0=\u00a01024\u00a0\n<\/code><\/pre>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u5982\u679cmax_length_for_sort_data\u503c\u592a\u4f4e\uff0c\u5219mysql\u4f1a\u81ea\u52a8\u4ece \u5355\u8def-&gt;\u53cc\u8def(\u592a\u4f4e\uff1a\u9700\u8981\u6392\u5e8f\u7684\u5217\u7684\u603b\u5927\u5c0f\u8d85\u8fc7\u4e86max_length_for_sort_data\u5b9a\u4e49\u7684\u5b57\u8282\u6570)<\/p>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\"><strong>\u2460 \u63d0\u9ad8order by\u67e5\u8be2\u7684\u7b56\u7565\uff1a<\/strong><\/p>\n<ul class=\"list-paddingleft-1\" style=\"margin-top: 8px; margin-bottom: 8px; padding-left: 25px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u9009\u62e9\u4f7f\u7528\u5355\u8def\u3001\u53cc\u8def \uff1b\u8c03\u6574buffer\u7684\u5bb9\u91cf\u5927\u5c0f<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u907f\u514d\u4f7f\u7528select * \u2026\uff08select\u540e\u9762\u5199\u6240\u6709\u5b57\u6bb5\uff0c\u4e5f\u6bd4\u5199*\u6548\u7387\u9ad8\uff09<\/section>\n<\/li>\n<li>\n<section style=\"margin-top: 5px; margin-bottom: 5px; line-height: 26px; color: #010101;\">\u590d\u5408\u7d22\u5f15\uff0c\u4e0d\u8981\u8de8\u5217\u4f7f\u7528 \uff0c\u907f\u514dusing filesort\u4fdd\u8bc1\u5168\u90e8\u7684\u6392\u5e8f\u5b57\u6bb5\uff0c\u6392\u5e8f\u7684\u4e00\u81f4\u6027\uff08\u90fd\u662f\u5347\u5e8f\u6216\u964d\u5e8f\uff09<\/section>\n<\/li>\n<\/ul>\n<p style=\"padding-top: 8px; padding-bottom: 8px; line-height: 26px;\" data-tool=\"mdnice\u7f16\u8f91\u5668\">\u7bc7\u5e45\u5f88\u957f\uff0c\u5185\u5bb9\u8f83\u591a\uff0c\u5efa\u8bae\u6536\u85cf\u3002<\/p>\n<\/section>\n<blockquote style=\"caret-color: #000000; font-family: -apple-system-font, system-ui, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif;\"><p><span style=\"font-size: 14px;\"><span style=\"color: #888888; font-family: 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', 'WenQuanYi Micro Hei', 'Helvetica Neue', Arial, sans-serif; font-size: 13px; letter-spacing: 0.544px; text-align: center; background-color: #ffffff;\">\u6765\u6e90\uff1a\u6570\u636e\u5206\u6790\u4e0d\u662f\u4e2a\u4e8b\u513f<\/span><\/span><\/p><\/blockquote>\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; color: #333333; font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; font-size: 17px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; text-align: center;\">\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; color: #333333; font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; font-size: 17px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; text-align: center;\"><span style=\"margin: 0px; padding: 0px; font-size: 15px; color: #888888;\">- EOF -<\/span><\/p>\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; color: #333333; font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; font-size: 17px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; text-align: center;\">\n<section style=\"margin: 0px 0px 0px 1em; padding: 0px; color: #333333; font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; font-size: 17px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: justify; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; max-width: 100%; line-height: 1.4; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 3px 8px; max-width: 100%; border-radius: 4px; color: #ffffff; background-color: #ff691f; font-family: inherit; text-align: inherit; text-decoration: inherit; font-size: 16px; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u63a8\u8350\u9605\u8bfb<\/span>\u00a0\u00a0<span style=\"margin: 0px 0px 0px 4px; padding: 3px 8px; max-width: 100%; border-radius: 1.2em; color: #ffffff; line-height: 1.2; background-color: #cccccc; font-family: inherit; text-align: inherit; text-decoration: inherit; border-color: #f96e57; font-size: 12px; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u70b9\u51fb\u6807\u9898\u53ef\u8df3\u8f6c<\/span><\/section>\n<section style=\"margin: -11px 0px 0px; padding: 22px 16px 16px; color: #333333; font-family: inherit; font-size: 1em; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: inherit; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: inherit; max-width: 100%; box-sizing: border-box !important; overflow-wrap: break-word !important; border: 1px solid #ff691f;\">\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; max-width: 100%; line-height: 2em; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; text-decoration: underline; font-size: 13px;\">1\u3001<a href=\"http:\/\/mp.weixin.qq.com\/s?__biz=MzA5ODM5MDU3MA==&amp;mid=2650889095&amp;idx=2&amp;sn=91ac0c2d979bdd28b912723f2eabb2eb&amp;chksm=8b67bcc2bc1035d43ae4f1baa2b00c27dd6ecc261023a40ceaf02d0053512f04d7ed94952791&amp;scene=21#wechat_redirect\" target=\"_blank\" rel=\"noopener\" data-itemshowtype=\"0\" data-linktype=\"2\" rel=\"nofollow\" >SQL \u4f18\u5316 20 \u8fde\u95ee<\/a><\/span><\/p>\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; max-width: 100%; line-height: 2em; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; text-decoration: underline; font-size: 13px;\">2\u3001<a href=\"http:\/\/mp.weixin.qq.com\/s?__biz=MzA5ODM5MDU3MA==&amp;mid=2650887048&amp;idx=1&amp;sn=396c71c3839ca715b9ca47d1ac152907&amp;chksm=8b67b4cdbc103ddb48bdd4b9ba4a1df902ab7b8f1330a46c6ea625d3e48ea4b6b5de5dee458f&amp;scene=21#wechat_redirect\" target=\"_blank\" rel=\"noopener\" data-itemshowtype=\"0\" data-linktype=\"2\" rel=\"nofollow\" >\u4e3a\u4ec0\u4e48\u4e0d\u5efa\u8bae\u5728 MySQL \u4e2d\u4f7f\u7528 UTF-8 ?<\/a><\/span><\/p>\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; max-width: 100%; line-height: 2em; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; text-decoration: underline; font-size: 13px;\">3\u3001<a style=\"font-size: 13px; letter-spacing: normal; white-space: normal;\" href=\"http:\/\/mp.weixin.qq.com\/s?__biz=MzA5ODM5MDU3MA==&amp;mid=2650887072&amp;idx=1&amp;sn=b497f97715e207dabb26d792ed1f20af&amp;chksm=8b67b4e5bc103df3afc6c1d97b1555fbae2d5c59407cfa80752329b20655c8ca4f25b5f632b2&amp;scene=21#wechat_redirect\" target=\"_blank\" rel=\"noopener\" data-itemshowtype=\"11\" data-linktype=\"2\" rel=\"nofollow\" >10.6K Star\uff01\u9177\u70ab\u7684\u5f00\u6e90\u6570\u636e\u5e93\u7ba1\u7406\u5de5\u5177\uff01<\/a><\/span><\/p>\n<\/section>\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; color: #333333; font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; font-size: 17px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: justify; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;\">\n<p style=\"margin: 0px; padding: 0px; clear: both; min-height: 1em; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; font-size: 16px; max-width: 100%; font-family: -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; color: #3e3e3e; background-color: #ffffff; text-align: center; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; max-width: 100%; color: #ffa900; font-size: 15px; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u770b\u5b8c\u672c\u6587\u6709\u6536\u83b7\uff1f\u8bf7\u8f6c\u53d1\u5206\u4eab\u7ed9\u66f4\u591a\u4eba<\/span><\/p>\n<section style=\"margin: 0px 0px 8px; padding: 0px; clear: both; min-height: 1em; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; font-size: 16px; max-width: 100%; font-family: -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; color: #3e3e3e; background-color: #ffffff; line-height: 25.6px; text-align: center; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; max-width: 100%; font-size: 15px; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><strong style=\"margin: 0px; padding: 0px; max-width: 100%; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; max-width: 100%; color: #ffa900; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u63a8\u8350\u5173\u6ce8\u300c\u6570\u636e\u5206\u6790\u4e0e\u5f00\u53d1\u300d\uff0c\u63d0\u5347\u6570\u636e\u6280\u80fd<\/span><\/strong><\/span><\/section>\n<section class=\"mp_profile_iframe_wrp\"><\/section>\n<p style=\"margin: 0px; padding: 0px; min-height: 1em; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial; font-size: 16px; max-width: 100%; font-family: -apple-system-font, BlinkMacSystemFont, 'Helvetica Neue', 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei UI', 'Microsoft YaHei', Arial, sans-serif; letter-spacing: 0.544px; color: #3e3e3e; background-color: #ffffff; text-align: right; box-sizing: border-box !important; overflow-wrap: break-word !important;\"><span style=\"margin: 0px; padding: 0px; letter-spacing: 0.544px; caret-color: #333333; max-width: 100%; font-size: 14px; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u70b9\u8d5e\u548c\u5728\u770b\u5c31\u662f\u6700\u5927\u7684\u652f\u6301<\/span><span style=\"margin: 0px; padding: 0px; letter-spacing: 0.544px; caret-color: #333333; max-width: 100%; font-size: 14px; box-sizing: border-box !important; overflow-wrap: break-word !important;\">\u2764\ufe0f<\/span><\/p>\n<p style=\"display: none;\">\n<blockquote><p>\u672c\u7bc7\u6587\u7ae0\u6765\u6e90\u4e8e\u5fae\u4fe1\u516c\u4f17\u53f7: \u6570\u636e\u5206\u6790\u4e0e\u5f00\u53d1<\/p><\/blockquote>\n<\/div>\n","raw":"","protected":false},"excerpt":{"rendered":"<p>\u2193\u63a8\u8350\u5173\u6ce8\u2193 \u5206\u4eab\u4e00\u7bc7\u5173\u4e8eSQL\u4f18\u5316\u7684\u786c\u6838\u6587\u7ae0\uff0c\u5168\u6587\u6709\u70b9\u957f\uff0c\u5efa\u8bae\u6536\u85cf\u540e\u6162\u6162\u770b\u3002 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