{"id":193969,"date":"2024-11-13T02:40:20","date_gmt":"2024-11-12T18:40:20","guid":{"rendered":"https:\/\/server.hk\/cnblog\/193969\/"},"modified":"2024-11-13T02:40:21","modified_gmt":"2024-11-12T18:40:21","slug":"%e4%b8%80%e5%88%86%e9%90%98%e5%b8%b6%e4%bd%a0%e5%ad%b8%e6%9c%83mysql%e8%a6%86%e8%93%8b%e7%b4%a2%e5%bc%95%ef%bc%8c%e8%ae%93%e4%bd%a0%e7%9a%84sql%e6%9b%b4%e9%ab%98%e6%95%88","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/193969\/","title":{"rendered":"\u4e00\u5206\u9418\u5e36\u4f60\u5b78\u6703MySQL\u8986\u84cb\u7d22\u5f15\uff0c\u8b93\u4f60\u7684SQL\u66f4\u9ad8\u6548"},"content":{"rendered":"<h1 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id=\"%e4%bb%80%e9%ba%bc%e6%98%af%e8%a6%86%e8%93%8b%e7%b4%a2%e5%bc%95%ef%bc%9f-vSVAwNmhjE\">\u4ec0\u9ebc\u662f\u8986\u84cb\u7d22\u5f15\uff1f<\/h2>\n<p>\u8986\u84cb\u7d22\u5f15\u662f\u6307\u4e00\u500b\u7d22\u5f15\u5305\u542b\u4e86\u67e5\u8a62\u6240\u9700\u7684\u6240\u6709\u5217\uff0c\u9019\u6a23\u5728\u57f7\u884c\u67e5\u8a62\u6642\uff0c\u6578\u64da\u5eab\u53ef\u4ee5\u76f4\u63a5\u5f9e\u7d22\u5f15\u4e2d\u7372\u53d6\u6240\u9700\u7684\u6578\u64da\uff0c\u800c\u7121\u9700\u56de\u8868\u67e5\u8a62\u539f\u59cb\u6578\u64da\u884c\u3002\u9019\u6a23\u4e0d\u50c5\u6e1b\u5c11\u4e86I\/O\u64cd\u4f5c\uff0c\u9084\u80fd\u63d0\u9ad8\u67e5\u8a62\u901f\u5ea6\u3002<\/p>\n<h2 id=\"%e8%a6%86%e8%93%8b%e7%b4%a2%e5%bc%95%e7%9a%84%e4%bd%bf%e7%94%a8%e5%a0%b4%e6%99%af-vSVAwNmhjE\">\u8986\u84cb\u7d22\u5f15\u7684\u4f7f\u7528\u5834\u666f<\/h2>\n<p>\u8986\u84cb\u7d22\u5f15\u7279\u5225\u9069\u5408\u4ee5\u4e0b\u5e7e\u7a2e\u60c5\u6cc1\uff1a<\/p>\n<ul>\n<li><strong>\u67e5\u8a62\u983b\u7e41\u7684\u5217\uff1a<\/strong>\u5982\u679c\u67d0\u4e9b\u5217\u7d93\u5e38\u88ab\u67e5\u8a62\uff0c\u5247\u53ef\u4ee5\u8003\u616e\u70ba\u9019\u4e9b\u5217\u5275\u5efa\u8986\u84cb\u7d22\u5f15\u3002<\/li>\n<li><strong>\u7be9\u9078\u548c\u6392\u5e8f\u64cd\u4f5c\uff1a<\/strong>\u7576\u67e5\u8a62\u4e2d\u5305\u542bWHERE\u689d\u4ef6\u548cORDER BY\u5b50\u53e5\u6642\uff0c\u8986\u84cb\u7d22\u5f15\u53ef\u4ee5\u986f\u8457\u63d0\u9ad8\u6027\u80fd\u3002<\/li>\n<li><strong>\u805a\u5408\u67e5\u8a62\uff1a<\/strong>\u5728\u9032\u884cSUM\u3001COUNT\u7b49\u805a\u5408\u64cd\u4f5c\u6642\uff0c\u8986\u84cb\u7d22\u5f15\u80fd\u5920\u52a0\u901f\u8a08\u7b97\u904e\u7a0b\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%a6%82%e4%bd%95%e5%89%b5%e5%bb%ba%e8%a6%86%e8%93%8b%e7%b4%a2%e5%bc%95-vSVAwNmhjE\">\u5982\u4f55\u5275\u5efa\u8986\u84cb\u7d22\u5f15<\/h2>\n<p>\u5275\u5efa\u8986\u84cb\u7d22\u5f15\u7684\u8a9e\u6cd5\u8207\u666e\u901a\u7d22\u5f15\u76f8\u4f3c\uff0c\u53ea\u9700\u5728\u7d22\u5f15\u4e2d\u5305\u542b\u6240\u6709\u67e5\u8a62\u6240\u9700\u7684\u5217\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u793a\u4f8b\uff1a<\/p>\n<pre><code>CREATE INDEX idx_covering ON employees (department_id, salary, name);<\/code><\/pre>\n<p>\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0c\u6211\u5011\u70baemployees\u8868\u5275\u5efa\u4e86\u4e00\u500b\u8986\u84cb\u7d22\u5f15\uff0c\u5305\u542b\u4e86department_id\u3001salary\u548cname\u4e09\u500b\u5217\u3002\u9019\u6a23\uff0c\u7576\u6211\u5011\u57f7\u884c\u4ee5\u4e0b\u67e5\u8a62\u6642\uff0c\u6578\u64da\u5eab\u53ef\u4ee5\u76f4\u63a5\u5f9e\u7d22\u5f15\u4e2d\u7372\u53d6\u7d50\u679c\uff1a<\/p>\n<pre><code>SELECT name FROM employees WHERE department_id = 1 ORDER BY salary DESC;<\/code><\/pre>\n<h2 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