{"id":11494,"date":"2025-06-12T11:24:21","date_gmt":"2025-06-12T03:24:21","guid":{"rendered":"https:\/\/egonlin.com\/?p=11494"},"modified":"2025-06-12T16:24:07","modified_gmt":"2025-06-12T08:24:07","slug":"%e6%9f%a5%e8%af%a2%e4%bc%98%e5%8c%96%e7%a5%9e%e5%99%a8-explain","status":"publish","type":"post","link":"https:\/\/egonlin.com\/?p=11494","title":{"rendered":"\u67e5\u8be2\u4f18\u5316\u795e\u5668-explain"},"content":{"rendered":"<p><strong>\u5173\u4e8eexplain\u547d\u4ee4\u76f8\u4fe1\u5927\u5bb6\u5e76\u4e0d\u964c\u751f\uff0c\u5177\u4f53\u7528\u6cd5\u548c\u5b57\u6bb5\u542b\u4e49\u53ef\u4ee5\u53c2\u8003\u5b98\u7f51<a href=\"http:\/\/dev.mysql.com\/doc\/refman\/5.5\/en\/explain-output.html\" rel=\"noopener nofollow\">explain-output<\/a>\uff0c\u8fd9\u91cc\u9700\u8981\u5f3a\u8c03rows\u662f\u6838\u5fc3\u6307\u6807\uff0c\u7edd\u5927\u90e8\u5206rows\u5c0f\u7684\u8bed\u53e5\u6267\u884c\u4e00\u5b9a\u5f88\u5feb\uff08\u6709\u4f8b\u5916\uff0c\u4e0b\u9762\u4f1a\u8bb2\u5230\uff09\u3002\u6240\u4ee5\u4f18\u5316\u8bed\u53e5\u57fa\u672c\u4e0a\u90fd\u662f\u5728\u4f18\u5316rows\u3002<\/strong><\/p>\n<div class=\"cnblogs_code\">\n<pre>\u6267\u884c\u8ba1\u5212\uff1a\u8ba9mysql\u9884\u4f30\u6267\u884c\u64cd\u4f5c(\u4e00\u822c\u6b63\u786e)\r\n    all &lt; index &lt; range &lt; index_merge &lt; ref_or_null &lt; ref &lt; eq_ref &lt; const &lt; system &lt; NULL<\/pre>\n<pre>    \r\n    \u6162\uff1a\r\n        select * from userinfo3 where name='alex'\r\n        \r\n        explain select * from userinfo3 where name='alex'\r\n        type: ALL(\u5168\u8868\u626b\u63cf)\r\n            select * from userinfo3 limit 1;\r\n    \u5feb\uff1a\r\n        select * from userinfo3 where email='alex'\r\n        type: const(\u8d70\u7d22\u5f15)<\/pre>\n<\/div>\n<div class=\"cnblogs_code\"><span class=\"cnblogs_code_collapse\">explain\u5b57\u6bb5\u8be6\u89e3<\/span><\/div>\n<div>\n<pre>1. id\uff1a\r\n\r\n\u5305\u542b\u4e00\u7ec4\u6570\u5b57\uff0c\u8868\u793a\u67e5\u8be2\u4e2d\u6267\u884cselect\u5b50\u53e5\u6216\u64cd\u4f5c\u8868\u7684\u987a\u5e8f\r\n\r\nExample\uff08id\u76f8\u540c\uff0c\u6267\u884c\u987a\u5e8f\u7531\u4e0a\u81f3\u4e0b\uff09\r\n\r\n\u5982\u679c\u662f\u5b50\u67e5\u8be2\uff0cid\u7684\u5e8f\u53f7\u4f1a\u9012\u589e\uff0cid\u503c\u8d8a\u5927\u4f18\u5148\u7ea7\u8d8a\u9ad8\uff0c\u8d8a\u5148\u88ab\u6267\u884c\r\n\r\nid\u5982\u679c\u76f8\u540c\uff0c\u53ef\u4ee5\u8ba4\u4e3a\u662f\u4e00\u7ec4\uff0c\u4ece\u4e0a\u5f80\u4e0b\u987a\u5e8f\u6267\u884c\uff1b\u5728\u6240\u6709\u7ec4\u4e2d\uff0cid\u503c\u8d8a\u5927\uff0c\u4f18\u5148\u7ea7\u8d8a\u9ad8\uff0c\u8d8a\u5148\u6267\u884c\r\n\r\n2. select_type\r\n\r\n\u793a\u67e5\u8be2\u4e2d\u6bcf\u4e2aselect\u5b50\u53e5\u7684\u7c7b\u578b\uff08\u7b80\u5355OR\u590d\u6742\uff09\r\n\r\na. SIMPLE\uff1a\u67e5\u8be2\u4e2d\u4e0d\u5305\u542b\u5b50\u67e5\u8be2\u6216\u8005UNION\r\nb. \u67e5\u8be2\u4e2d\u82e5\u5305\u542b\u4efb\u4f55\u590d\u6742\u7684\u5b50\u90e8\u5206\uff0c\u6700\u5916\u5c42\u67e5\u8be2\u5219\u88ab\u6807\u8bb0\u4e3a\uff1aPRIMARY\r\nc. \u5728SELECT\u6216WHERE\u5217\u8868\u4e2d\u5305\u542b\u4e86\u5b50\u67e5\u8be2\uff0c\u8be5\u5b50\u67e5\u8be2\u88ab\u6807\u8bb0\u4e3a\uff1aSUBQUERY\r\nd. \u5728FROM\u5217\u8868\u4e2d\u5305\u542b\u7684\u5b50\u67e5\u8be2\u88ab\u6807\u8bb0\u4e3a\uff1aDERIVED\uff08\u884d\u751f\uff09\u7528\u6765\u8868\u793a\u5305\u542b\u5728from\u5b50\u53e5\u4e2d\u7684\u5b50\u67e5\u8be2\u7684select\uff0cmysql\u4f1a\u9012\u5f52\u6267\u884c\u5e76\u5c06\u7ed3\u679c\u653e\u5230\u4e00\u4e2a\u4e34\u65f6\u8868\u4e2d\u3002\u670d\u52a1\u5668\u5185\u90e8\u79f0\u4e3a\"\u6d3e\u751f\u8868\"\uff0c\u56e0\u4e3a\u8be5\u4e34\u65f6\u8868\u662f\u4ece\u5b50\u67e5\u8be2\u4e2d\u6d3e\u751f\u51fa\u6765\u7684\r\ne. \u82e5\u7b2c\u4e8c\u4e2aSELECT\u51fa\u73b0\u5728UNION\u4e4b\u540e\uff0c\u5219\u88ab\u6807\u8bb0\u4e3aUNION\uff1b\u82e5UNION\u5305\u542b\u5728FROM\u5b50\u53e5\u7684\u5b50\u67e5\u8be2\u4e2d\uff0c\u5916\u5c42SELECT\u5c06\u88ab\u6807\u8bb0\u4e3a\uff1aDERIVED\r\nf. \u4eceUNION\u8868\u83b7\u53d6\u7ed3\u679c\u7684SELECT\u88ab\u6807\u8bb0\u4e3a\uff1aUNION RESULT\r\n\r\nSUBQUERY\u548cUNION\u8fd8\u53ef\u4ee5\u88ab\u6807\u8bb0\u4e3aDEPENDENT\u548cUNCACHEABLE\u3002\r\nDEPENDENT\u610f\u5473\u7740select\u4f9d\u8d56\u4e8e\u5916\u5c42\u67e5\u8be2\u4e2d\u53d1\u73b0\u7684\u6570\u636e\u3002\r\nUNCACHEABLE\u610f\u5473\u7740select\u4e2d\u7684\u67d0\u4e9b \u7279\u6027\u963b\u6b62\u7ed3\u679c\u88ab\u7f13\u5b58\u4e8e\u4e00\u4e2aitem_cache\u4e2d\u3002\r\n\r\n\u7b2c\u4e00\u884c\uff1aid\u5217\u4e3a1\uff0c\u8868\u793a\u7b2c\u4e00\u4e2aselect\uff0cselect_type\u5217\u7684primary\u8868 \u793a\u8be5\u67e5\u8be2\u4e3a\u5916\u5c42\u67e5\u8be2\uff0ctable\u5217\u88ab\u6807\u8bb0\u4e3a&lt;derived3&gt;\uff0c\u8868\u793a\u67e5\u8be2\u7ed3\u679c\u6765\u81ea\u4e00\u4e2a\u884d\u751f\u8868\uff0c\u5176\u4e2d3\u4ee3\u8868\u8be5\u67e5\u8be2\u884d\u751f\u81ea\u7b2c\u4e09\u4e2aselect\u67e5\u8be2\uff0c\u5373id\u4e3a3\u7684select\u3002\r\n\u7b2c\u4e8c\u884c\uff1aid\u4e3a3\uff0c\u8868\u793a\u8be5\u67e5\u8be2\u7684\u6267\u884c\u6b21\u5e8f\u4e3a2\uff08 4 =&gt; 3\uff09\uff0c\u662f\u6574\u4e2a\u67e5\u8be2\u4e2d\u7b2c\u4e09\u4e2aselect\u7684\u4e00\u90e8\u5206\u3002\u56e0\u67e5\u8be2\u5305\u542b\u5728from\u4e2d\uff0c\u6240\u4ee5\u4e3aderived\u3002\r\n\u7b2c\u4e09\u884c\uff1aselect\u5217\u8868\u4e2d\u7684\u5b50\u67e5\u8be2\uff0cselect_type\u4e3asubquery\uff0c\u4e3a\u6574\u4e2a\u67e5\u8be2\u4e2d\u7684\u7b2c\u4e8c\u4e2aselect\u3002\r\n\u7b2c\u56db\u884c\uff1aselect_type\u4e3aunion\uff0c\u8bf4\u660e\u7b2c\u56db\u4e2aselect\u662funion\u91cc\u7684\u7b2c\u4e8c\u4e2aselect\uff0c\u6700\u5148\u6267\u884c\u3002\r\n\u7b2c\u4e94\u884c\uff1a\u4ee3\u8868\u4eceunion\u7684\u4e34\u65f6\u8868\u4e2d\u8bfb\u53d6\u884c\u7684\u9636\u6bb5\uff0ctable\u5217\u7684&lt;union1,4&gt;\u8868\u793a\u7528\u7b2c\u4e00\u4e2a\u548c\u7b2c\u56db\u4e2aselect\u7684\u7ed3\u679c\u8fdb\u884cunion\u64cd\u4f5c\u3002\r\n\r\n3\u3001 type   \r\n\r\n\u8868\u793aMySQL\u5728\u8868\u4e2d\u627e\u5230\u6240\u9700\u884c\u7684\u65b9\u5f0f\uff0c\u53c8\u79f0\u201c\u8bbf\u95ee\u7c7b\u578b\u201d\u3002\r\n\r\n\u5e38\u7528\u7684\u7c7b\u578b\u6709\uff1a ALL, index,  range, ref, eq_ref, const, system, NULL\uff08\u4ece\u5de6\u5230\u53f3\uff0c\u6027\u80fd\u4ece\u5dee\u5230\u597d\uff09\r\n\r\nALL\uff1aFull Table Scan\uff0c MySQL\u5c06\u904d\u5386\u5168\u8868\u4ee5\u627e\u5230\u5339\u914d\u7684\u884c\r\n\r\nindex: Full Index Scan\uff0cindex\u4e0eALL\u533a\u522b\u4e3aindex\u7c7b\u578b\u53ea\u904d\u5386\u7d22\u5f15\u6811\r\n\r\nrange:\u53ea\u68c0\u7d22\u7ed9\u5b9a\u8303\u56f4\u7684\u884c\uff0c\u4f7f\u7528\u4e00\u4e2a\u7d22\u5f15\u6765\u9009\u62e9\u884c\r\n\r\nref: \u8868\u793a\u4e0a\u8ff0\u8868\u7684\u8fde\u63a5\u5339\u914d\u6761\u4ef6\uff0c\u5373\u54ea\u4e9b\u5217\u6216\u5e38\u91cf\u88ab\u7528\u4e8e\u67e5\u627e\u7d22\u5f15\u5217\u4e0a\u7684\u503c\r\n\r\neq_ref: \u7c7b\u4f3cref\uff0c\u533a\u522b\u5c31\u5728\u4f7f\u7528\u7684\u7d22\u5f15\u662f\u552f\u4e00\u7d22\u5f15\uff0c\u5bf9\u4e8e\u6bcf\u4e2a\u7d22\u5f15\u952e\u503c\uff0c\u8868\u4e2d\u53ea\u6709\u4e00\u6761\u8bb0\u5f55\u5339\u914d\uff0c\u7b80\u5355\u6765\u8bf4\uff0c\u5c31\u662f\u591a\u8868\u8fde\u63a5\u4e2d\u4f7f\u7528primary key\u6216\u8005 unique key\u4f5c\u4e3a\u5173\u8054\u6761\u4ef6\r\n\r\nconst\u3001system: \u5f53MySQL\u5bf9\u67e5\u8be2\u67d0\u90e8\u5206\u8fdb\u884c\u4f18\u5316\uff0c\u5e76\u8f6c\u6362\u4e3a\u4e00\u4e2a\u5e38\u91cf\u65f6\uff0c\u4f7f\u7528\u8fd9\u4e9b\u7c7b\u578b\u8bbf\u95ee\u3002\u5982\u5c06\u4e3b\u952e\u7f6e\u4e8ewhere\u5217\u8868\u4e2d\uff0cMySQL\u5c31\u80fd\u5c06\u8be5\u67e5\u8be2\u8f6c\u6362\u4e3a\u4e00\u4e2a\u5e38\u91cf,system\u662fconst\u7c7b\u578b\u7684\u7279\u4f8b\uff0c\u5f53\u67e5\u8be2\u7684\u8868\u53ea\u6709\u4e00\u884c\u7684\u60c5\u51b5\u4e0b\uff0c\u4f7f\u7528system\r\n\r\nNULL: MySQL\u5728\u4f18\u5316\u8fc7\u7a0b\u4e2d\u5206\u89e3\u8bed\u53e5\uff0c\u6267\u884c\u65f6\u751a\u81f3\u4e0d\u7528\u8bbf\u95ee\u8868\u6216\u7d22\u5f15\uff0c\u4f8b\u5982\u4ece\u4e00\u4e2a\u7d22\u5f15\u5217\u91cc\u9009\u53d6\u6700\u5c0f\u503c\u53ef\u4ee5\u901a\u8fc7\u5355\u72ec\u7d22\u5f15\u67e5\u627e\u5b8c\u6210\u3002\r\n\r\n4\u3001table\r\n\r\n\u663e\u793a\u8fd9\u4e00\u884c\u7684\u6570\u636e\u662f\u5173\u4e8e\u54ea\u5f20\u8868\u7684\uff0c\u6709\u65f6\u4e0d\u662f\u771f\u5b9e\u7684\u8868\u540d\u5b57,\u770b\u5230\u7684\u662fderivedx(x\u662f\u4e2a\u6570\u5b57,\u6211\u7684\u7406\u89e3\u662f\u7b2c\u51e0\u6b65\u6267\u884c\u7684\u7ed3\u679c)\r\n\r\n5\u3001possible_keys\r\n\r\n\u6307\u51faMySQL\u80fd\u4f7f\u7528\u54ea\u4e2a\u7d22\u5f15\u5728\u8868\u4e2d\u627e\u5230\u8bb0\u5f55\uff0c\u67e5\u8be2\u6d89\u53ca\u5230\u7684\u5b57\u6bb5\u4e0a\u82e5\u5b58\u5728\u7d22\u5f15\uff0c\u5219\u8be5\u7d22\u5f15\u5c06\u88ab\u5217\u51fa\uff0c\u4f46\u4e0d\u4e00\u5b9a\u88ab\u67e5\u8be2\u4f7f\u7528\r\n\r\n\u8be5\u5217\u5b8c\u5168\u72ec\u7acb\u4e8eEXPLAIN\u8f93\u51fa\u6240\u793a\u7684\u8868\u7684\u6b21\u5e8f\u3002\u8fd9\u610f\u5473\u7740\u5728possible_keys\u4e2d\u7684\u67d0\u4e9b\u952e\u5b9e\u9645\u4e0a\u4e0d\u80fd\u6309\u751f\u6210\u7684\u8868\u6b21\u5e8f\u4f7f\u7528\u3002\r\n\u5982\u679c\u8be5\u5217\u662fNULL\uff0c\u5219\u6ca1\u6709\u76f8\u5173\u7684\u7d22\u5f15\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u53ef\u4ee5\u901a\u8fc7\u68c0\u67e5WHERE\u5b50\u53e5\u770b\u662f\u5426\u5b83\u5f15\u7528\u67d0\u4e9b\u5217\u6216\u9002\u5408\u7d22\u5f15\u7684\u5217\u6765\u63d0\u9ad8\u4f60\u7684\u67e5\u8be2\u6027\u80fd\u3002\u5982\u679c\u662f\u8fd9\u6837\uff0c\u521b\u9020\u4e00\u4e2a\u9002\u5f53\u7684\u7d22\u5f15\u5e76\u4e14\u518d\u6b21\u7528EXPLAIN\u68c0\u67e5\u67e5\u8be2\r\n\r\n6\u3001Key      key\u5217\u663e\u793aMySQL\u5b9e\u9645\u51b3\u5b9a\u4f7f\u7528\u7684\u952e\uff08\u7d22\u5f15\uff09\r\n\r\n\u5982\u679c\u6ca1\u6709\u9009\u62e9\u7d22\u5f15\uff0c\u952e\u662fNULL\u3002\u8981\u60f3\u5f3a\u5236MySQL\u4f7f\u7528\u6216\u5ffd\u89c6possible_keys\u5217\u4e2d\u7684\u7d22\u5f15\uff0c\u5728\u67e5\u8be2\u4e2d\u4f7f\u7528FORCE INDEX\u3001USE INDEX\u6216\u8005IGNORE INDEX\u3002\uff08\u6ce8\uff1a\u7d22\u5f15\u662f\u5426\u547d\u4e2d\uff09\r\n\r\n7\u3001key_len\r\n\r\n\u8868\u793a\u7d22\u5f15\u4e2d\u4f7f\u7528\u7684\u5b57\u8282\u6570\uff0c\u53ef\u901a\u8fc7\u8be5\u5217\u8ba1\u7b97\u67e5\u8be2\u4e2d\u4f7f\u7528\u7684\u7d22\u5f15\u7684\u957f\u5ea6\uff08key_len\u663e\u793a\u7684\u503c\u4e3a\u7d22\u5f15\u5b57\u6bb5\u7684\u6700\u5927\u53ef\u80fd\u957f\u5ea6\uff0c\u5e76\u975e\u5b9e\u9645\u4f7f\u7528\u957f\u5ea6\uff0c\u5373key_len\u662f\u6839\u636e\u8868\u5b9a\u4e49\u8ba1\u7b97\u800c\u5f97\uff0c\u4e0d\u662f\u901a\u8fc7\u8868\u5185\u68c0\u7d22\u51fa\u7684\uff09\r\n\r\n\u4e0d\u635f\u5931\u7cbe\u786e\u6027\u7684\u60c5\u51b5\u4e0b\uff0c\u957f\u5ea6\u8d8a\u77ed\u8d8a\u597d  \r\n\r\n8\u3001ref\r\n\r\n\u8868\u793a\u4e0a\u8ff0\u8868\u7684\u8fde\u63a5\u5339\u914d\u6761\u4ef6\uff0c\u5373\u54ea\u4e9b\u5217\u6216\u5e38\u91cf\u88ab\u7528\u4e8e\u67e5\u627e\u7d22\u5f15\u5217\u4e0a\u7684\u503c \r\n\r\n9\u3001rows\r\n\r\n \u8868\u793aMySQL\u6839\u636e\u8868\u7edf\u8ba1\u4fe1\u606f\u53ca\u7d22\u5f15\u9009\u7528\u60c5\u51b5\uff0c\u4f30\u7b97\u7684\u627e\u5230\u6240\u9700\u7684\u8bb0\u5f55\u6240\u9700\u8981\u8bfb\u53d6\u7684\u884c\u6570\r\n\r\n10\u3001Extra\r\n\r\n\u8be5\u5217\u5305\u542bMySQL\u89e3\u51b3\u67e5\u8be2\u7684\u8be6\u7ec6\u4fe1\u606f,\u6709\u4ee5\u4e0b\u51e0\u79cd\u60c5\u51b5\uff1a\r\n\r\nUsing where:\u5217\u6570\u636e\u662f\u4ece\u4ec5\u4ec5\u4f7f\u7528\u4e86\u7d22\u5f15\u4e2d\u7684\u4fe1\u606f\u800c\u6ca1\u6709\u8bfb\u53d6\u5b9e\u9645\u7684\u884c\u52a8\u7684\u8868\u8fd4\u56de\u7684\uff0c\u8fd9\u53d1\u751f\u5728\u5bf9\u8868\u7684\u5168\u90e8\u7684\u8bf7\u6c42\u5217\u90fd\u662f\u540c\u4e00\u4e2a\u7d22\u5f15\u7684\u90e8\u5206\u7684\u65f6\u5019\uff0c\u8868\u793amysql\u670d\u52a1\u5668\u5c06\u5728\u5b58\u50a8\u5f15\u64ce\u68c0\u7d22\u884c\u540e\u518d\u8fdb\u884c\u8fc7\u6ee4\r\n\r\nUsing temporary\uff1a\u8868\u793aMySQL\u9700\u8981\u4f7f\u7528\u4e34\u65f6\u8868\u6765\u5b58\u50a8\u7ed3\u679c\u96c6\uff0c\u5e38\u89c1\u4e8e\u6392\u5e8f\u548c\u5206\u7ec4\u67e5\u8be2\r\n\r\nUsing filesort\uff1aMySQL\u4e2d\u65e0\u6cd5\u5229\u7528\u7d22\u5f15\u5b8c\u6210\u7684\u6392\u5e8f\u64cd\u4f5c\u79f0\u4e3a\u201c\u6587\u4ef6\u6392\u5e8f\u201d\r\n\r\nUsing join buffer\uff1a\u6539\u503c\u5f3a\u8c03\u4e86\u5728\u83b7\u53d6\u8fde\u63a5\u6761\u4ef6\u65f6\u6ca1\u6709\u4f7f\u7528\u7d22\u5f15\uff0c\u5e76\u4e14\u9700\u8981\u8fde\u63a5\u7f13\u51b2\u533a\u6765\u5b58\u50a8\u4e2d\u95f4\u7ed3\u679c\u3002\u5982\u679c\u51fa\u73b0\u4e86\u8fd9\u4e2a\u503c\uff0c\u90a3\u5e94\u8be5\u6ce8\u610f\uff0c\u6839\u636e\u67e5\u8be2\u7684\u5177\u4f53\u60c5\u51b5\u53ef\u80fd\u9700\u8981\u6dfb\u52a0\u7d22\u5f15\u6765\u6539\u8fdb\u80fd\u3002\r\n\r\nImpossible where\uff1a\u8fd9\u4e2a\u503c\u5f3a\u8c03\u4e86where\u8bed\u53e5\u4f1a\u5bfc\u81f4\u6ca1\u6709\u7b26\u5408\u6761\u4ef6\u7684\u884c\u3002\r\n\r\nSelect tables optimized away\uff1a\u8fd9\u4e2a\u503c\u610f\u5473\u7740\u4ec5\u901a\u8fc7\u4f7f\u7528\u7d22\u5f15\uff0c\u4f18\u5316\u5668\u53ef\u80fd\u4ec5\u4ece\u805a\u5408\u51fd\u6570\u7ed3\u679c\u4e2d\u8fd4\u56de\u4e00\u884c\u3002<\/pre>\n<\/div>\n<p><strong>\u4f8b1\uff1atype\u4e3aAll\uff0c\u4ee3\u8868\u5168\u90e8\u626b\u63cf<\/strong><\/p>\n<div class=\"cnblogs_code\">\n<pre>#1.\u4ec0\u4e48\u662f\u5168\u8868\u626b\u63cf\r\n\u5728explain\u8bed\u53e5\u7ed3\u679c\u4e2dtype\u4e3aALL\uff0cMySQL\u5c06\u904d\u5386\u5168\u8868\u4ee5\u627e\u5230\u5339\u914d\u7684\u884c\r\n\r\n#2.\u4ec0\u4e48\u65f6\u5019\u51fa\u73b0\u5168\u8868\u626b\u63cf?\r\n1.\u4e1a\u52a1\u786e\u5b9e\u8981\u83b7\u53d6\u6240\u6709\u6570\u636e\r\n    mysql&gt; explain select * from city;\r\n    \r\n#2.\u4e0d\u8d70\u7d22\u5f15\u5bfc\u81f4\u7684\u5168\u8868\u626b\u63cf\r\n#2.1 \u6ca1\u7d22\u5f15\r\nmysql&gt; explain select * from city where District='shanghai';\r\n\r\n\u521b\u5efa\u7d22\u5f15\u540e\u901f\u5ea6\u4f1a\u63d0\u5347\uff0c\u53d8\u6210\u7d22\u5f15\u626b\u63cf\u4e86\r\nmysql&gt; alter table city add index idx_District(District);\r\nmysql&gt; explain select * from city where District='shanghai';\r\n\r\n#2.2 \u7d22\u5f15\u521b\u5efa\u6709\u95ee\u9898\r\n#2.3 \u8bed\u53e5\u6709\u95ee\u9898<\/pre>\n<\/div>\n<p>&nbsp;<\/p>\n<p><strong>\u4f8b2\uff1a\u7d22\u5f15\u626b\u63cf<\/strong><\/p>\n<div class=\"cnblogs_code\">\n<pre>#\u5e38\u89c1\u7684\u7d22\u5f15\u626b\u63cf\u7c7b\u578b:\r\n1\uff09index \u5168\u7d22\u5f15\u626b\u63cf\r\nindex\u4e0eALL\u533a\u522b\u4e3aindex\u7c7b\u578b\u53ea\u904d\u5386\u7d22\u5f15\u6811\uff08\u6027\u80fd\u4e5f\u4e0d\u9ad8\uff09\r\nmysql&gt; explain select population from city;\r\n\r\n2\uff09range    \u8303\u56f4\u67e5\u8be2\r\n\u53ea\u68c0\u7d22\u7ed9\u5b9a\u8303\u56f4\u7684\u884c\uff0c\u4f7f\u7528\u4e00\u4e2a\u7d22\u5f15\u6765\u9009\u62e9\u884c\uff0c\u4e00\u822c\u6765\u8bf4\uff0cSQL\u8bed\u53e5\u53ea\u8981\u8fbe\u5230range\u7ea7\u522b\uff0c\u5c31\u53ef\u4ee5\u4e86\r\nmysql&gt; explain select * from city where countrycode in ('USA','CHN');\r\n\r\n3\uff09ref \u7cbe\u786e\u67e5\u627e\uff0c\u5339\u914d\u6761\u4ef6\u6709\u666e\u901a\u7d22\u5f15\r\n\u5148\u7ed9population\u5217\u4e00\u4e2a\u7d22\u5f15\r\nmysql&gt; alter table city add index idx_population(population);\r\n\u7136\u540e\u67e5\u8be2\r\nmysql&gt; explain select * from city where population=300000000;\r\n\r\n4\uff09eq_ref    \u7c7b\u4f3cref\r\n\u533a\u522b\u5c31\u5728\u4f7f\u7528\u7684\u7d22\u5f15\u662f\u552f\u4e00\u7d22\u5f15\r\nexplain select city.name,city.countrycode,country.name  from city join country on city.countrycode=country.code where city.population&lt;100;\r\n\r\n5\uff09const \u4f7f\u7528\u7684\u7d22\u5f15\u662f\u4e3b\u952e\u7d22\u5f15\r\nmysql&gt; explain select * from country where code='CHN';\r\n\r\n6\uff09system system\u662fconst\u7c7b\u578b\u7684\u7279\u4f8b,\u5f53\u67e5\u8be2\u7684\u8868\u53ea\u6709\u4e00\u884c\u7684\u60c5\u51b5\u4e0b\r\nmysql&gt; delete from country where code != 'CHN';\r\n\u6709\u5916\u952e\u5220\u9664\u4e0d\u4e86\r\n\r\n7\uff09null \u6267\u884c\u8fc7\u7a0b\u4e0d\u7528\u8bbf\u95ee\u8868\u6216\u7d22\u5f15\uff0c\u76f4\u63a5\u9009\u53d6\u7d22\u5f15\u5217\u7684\u6700\u5c0f\u503c\r\nmysql&gt; explain select min(population) from city;<\/pre>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u5173\u4e8eexplain\u547d\u4ee4\u76f8\u4fe1\u5927\u5bb6\u5e76\u4e0d\u964c\u751f\uff0c\u5177\u4f53\u7528\u6cd5\u548c\u5b57\u6bb5\u542b\u4e49\u53ef\u4ee5\u53c2\u8003\u5b98\u7f51explain-output\uff0c\u8fd9\u91cc\u9700\u8981\u5f3a [&hellip;]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts\/11494"}],"collection":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=11494"}],"version-history":[{"count":1,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts\/11494\/revisions"}],"predecessor-version":[{"id":11495,"href":"https:\/\/egonlin.com\/index.php?rest_route=\/wp\/v2\/posts\/11494\/revisions\/11495"}],"wp:attachment":[{"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11494"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11494"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/egonlin.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11494"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}