{"id":887,"date":"2015-08-09T17:58:48","date_gmt":"2015-08-09T09:58:48","guid":{"rendered":"http:\/\/www.royalwzy.com\/?p=887"},"modified":"2015-09-10T21:53:01","modified_gmt":"2015-09-10T13:53:01","slug":"mysql-explain","status":"publish","type":"post","link":"http:\/\/www.royalwzy.com\/?p=887","title":{"rendered":"MySQL EXPLAIN"},"content":{"rendered":"

explain\u663e\u793a\u4e86mysql\u5982\u4f55\u4f7f\u7528\u7d22\u5f15\u6765\u5904\u7406select\u8bed\u53e5\u4ee5\u53ca\u8fde\u63a5\u8868\u3002\u53ef\u4ee5\u5e2e\u52a9\u9009\u62e9\u66f4\u597d\u7684\u7d22\u5f15\u548c\u5199\u51fa\u66f4\u4f18\u5316\u7684\u67e5\u8be2\u8bed\u53e5\u3002<\/p>\n

\u4f7f\u7528\u65b9\u6cd5\uff0c\u5728select\u8bed\u53e5\u524d\u52a0\u4e0aexplain\u5c31\u53ef\u4ee5\u4e86\uff1a<\/p>\n

\u5982\uff1a<\/p>\n

    \n
  1. explain\u00a0select<\/strong>\u00a0surname,first_name\u00a0form\u00a0a,b\u00a0where<\/strong>\u00a0a.id=b.id<\/li>\n<\/ol>\n

    EXPLAIN\u5217\u7684\u89e3\u91ca\uff1a<\/strong><\/p>\n

    table\uff1a\u663e\u793a\u8fd9\u4e00\u884c\u7684\u6570\u636e\u662f\u5173\u4e8e\u54ea\u5f20\u8868\u7684<\/p>\n

    type\uff1a\u8fd9\u662f\u91cd\u8981\u7684\u5217\uff0c\u663e\u793a\u8fde\u63a5\u4f7f\u7528\u4e86\u4f55\u79cd\u7c7b\u578b\u3002\u4ece\u6700\u597d\u5230\u6700\u5dee\u7684\u8fde\u63a5\u7c7b\u578b\u4e3aconst\u3001eq_reg\u3001ref\u3001range\u3001indexhe\u548cALL<\/p>\n

    possible_keys\uff1a\u663e\u793a\u53ef\u80fd\u5e94\u7528\u5728\u8fd9\u5f20\u8868\u4e2d\u7684\u7d22\u5f15\u3002\u5982\u679c\u4e3a\u7a7a\uff0c\u6ca1\u6709\u53ef\u80fd\u7684\u7d22\u5f15\u3002\u53ef\u4ee5\u4e3a\u76f8\u5173\u7684\u57df\u4eceWHERE\u8bed\u53e5\u4e2d\u9009\u62e9\u4e00\u4e2a\u5408\u9002\u7684\u8bed\u53e5<\/p>\n

    key\uff1a \u5b9e\u9645\u4f7f\u7528\u7684\u7d22\u5f15\u3002\u5982\u679c\u4e3aNULL\uff0c\u5219\u6ca1\u6709\u4f7f\u7528\u7d22\u5f15\u3002\u5f88\u5c11\u7684\u60c5\u51b5\u4e0b\uff0cMYSQL\u4f1a\u9009\u62e9\u4f18\u5316\u4e0d\u8db3\u7684\u7d22\u5f15\u3002\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u53ef\u4ee5\u5728SELECT\u8bed\u53e5\u4e2d\u4f7f\u7528USE INDEX\uff08indexname\uff09\u6765\u5f3a\u5236\u4f7f\u7528\u4e00\u4e2a\u7d22\u5f15\u6216\u8005\u7528IGNORE INDEX\uff08indexname\uff09\u6765\u5f3a\u5236MYSQL\u5ffd\u7565\u7d22\u5f15<\/p>\n

    key_len\uff1a\u4f7f\u7528\u7684\u7d22\u5f15\u7684\u957f\u5ea6\u3002\u5728\u4e0d\u635f\u5931\u7cbe\u786e\u6027\u7684\u60c5\u51b5\u4e0b\uff0c\u957f\u5ea6\u8d8a\u77ed\u8d8a\u597d<\/p>\n

    ref\uff1a\u663e\u793a\u7d22\u5f15\u7684\u54ea\u4e00\u5217\u88ab\u4f7f\u7528\u4e86\uff0c\u5982\u679c\u53ef\u80fd\u7684\u8bdd\uff0c\u662f\u4e00\u4e2a\u5e38\u6570<\/p>\n

    rows\uff1aMYSQL\u8ba4\u4e3a\u5fc5\u987b\u68c0\u67e5\u7684\u7528\u6765\u8fd4\u56de\u8bf7\u6c42\u6570\u636e\u7684\u884c\u6570<\/p>\n

    Extra\uff1a\u5173\u4e8eMYSQL\u5982\u4f55\u89e3\u6790\u67e5\u8be2\u7684\u989d\u5916\u4fe1\u606f\u3002\u5c06\u5728\u88684.3\u4e2d\u8ba8\u8bba\uff0c\u4f46\u8fd9\u91cc\u53ef\u4ee5\u770b\u5230\u7684\u574f\u7684\u4f8b\u5b50\u662fUsing temporary\u548cUsing filesort\uff0c\u610f\u601dMYSQL\u6839\u672c\u4e0d\u80fd\u4f7f\u7528\u7d22\u5f15\uff0c\u7ed3\u679c\u662f\u68c0\u7d22\u4f1a\u5f88\u6162<\/p>\n

    extra\u5217\u8fd4\u56de\u7684\u63cf\u8ff0\u7684\u610f\u4e49<\/strong><\/p>\n

    Distinct:\u4e00\u65e6MYSQL\u627e\u5230\u4e86\u4e0e\u884c\u76f8\u8054\u5408\u5339\u914d\u7684\u884c\uff0c\u5c31\u4e0d\u518d\u641c\u7d22\u4e86<\/p>\n

    Not exists: MYSQL\u4f18\u5316\u4e86LEFT JOIN\uff0c\u4e00\u65e6\u5b83\u627e\u5230\u4e86\u5339\u914dLEFT JOIN\u6807\u51c6\u7684\u884c\uff0c\u5c31\u4e0d\u518d\u641c\u7d22\u4e86<\/p>\n

    Range checked for each Record\uff08index map:#\uff09:\u6ca1\u6709\u627e\u5230\u7406\u60f3\u7684\u7d22\u5f15\uff0c\u56e0\u6b64\u5bf9\u4e8e\u4ece\u524d\u9762\u8868\u4e2d\u6765\u7684\u6bcf\u4e00\u4e2a\u884c\u7ec4\u5408\uff0cMYSQL\u68c0\u67e5\u4f7f\u7528\u54ea\u4e2a\u7d22\u5f15\uff0c\u5e76\u7528\u5b83\u6765\u4ece\u8868\u4e2d\u8fd4\u56de\u884c\u3002\u8fd9\u662f\u4f7f\u7528\u7d22\u5f15\u7684\u6700\u6162\u7684\u8fde\u63a5\u4e4b\u4e00<\/p>\n

    Using filesort: \u770b\u5230\u8fd9\u4e2a\u7684\u65f6\u5019\uff0c\u67e5\u8be2\u5c31\u9700\u8981\u4f18\u5316\u4e86\u3002MYSQL\u9700\u8981\u8fdb\u884c\u989d\u5916\u7684\u6b65\u9aa4\u6765\u53d1\u73b0\u5982\u4f55\u5bf9\u8fd4\u56de\u7684\u884c\u6392\u5e8f\u3002\u5b83\u6839\u636e\u8fde\u63a5\u7c7b\u578b\u4ee5\u53ca\u5b58\u50a8\u6392\u5e8f\u952e\u503c\u548c\u5339\u914d\u6761\u4ef6\u7684\u5168\u90e8\u884c\u7684\u884c\u6307\u9488\u6765\u6392\u5e8f\u5168\u90e8\u884c<\/p>\n

    Using index: \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<\/p>\n

    Using temporary \u770b\u5230\u8fd9\u4e2a\u7684\u65f6\u5019\uff0c\u67e5\u8be2\u9700\u8981\u4f18\u5316\u4e86\u3002\u8fd9\u91cc\uff0cMYSQL\u9700\u8981\u521b\u5efa\u4e00\u4e2a\u4e34\u65f6\u8868\u6765\u5b58\u50a8\u7ed3\u679c\uff0c\u8fd9\u901a\u5e38\u53d1\u751f\u5728\u5bf9\u4e0d\u540c\u7684\u5217\u96c6\u8fdb\u884cORDER BY\u4e0a\uff0c\u800c\u4e0d\u662fGROUP BY\u4e0a<\/p>\n

    Where used \u4f7f\u7528\u4e86WHERE\u4ece\u53e5\u6765\u9650\u5236\u54ea\u4e9b\u884c\u5c06\u4e0e\u4e0b\u4e00\u5f20\u8868\u5339\u914d\u6216\u8005\u662f\u8fd4\u56de\u7ed9\u7528\u6237\u3002\u5982\u679c\u4e0d\u60f3\u8fd4\u56de\u8868\u4e2d\u7684\u5168\u90e8\u884c\uff0c\u5e76\u4e14\u8fde\u63a5\u7c7b\u578bALL\u6216index\uff0c\u8fd9\u5c31\u4f1a\u53d1\u751f\uff0c\u6216\u8005\u662f\u67e5\u8be2\u6709\u95ee\u9898\u4e0d\u540c\u8fde\u63a5\u7c7b\u578b\u7684\u89e3\u91ca\uff08\u6309\u7167\u6548\u7387\u9ad8\u4f4e\u7684\u987a\u5e8f\u6392\u5e8f\uff09<\/p>\n

    system \u8868\u53ea\u6709\u4e00\u884c\uff1asystem\u8868\u3002\u8fd9\u662fconst\u8fde\u63a5\u7c7b\u578b\u7684\u7279\u6b8a\u60c5\u51b5<\/p>\n

    const:\u8868\u4e2d\u7684\u4e00\u4e2a\u8bb0\u5f55\u7684\u6700\u5927\u503c\u80fd\u591f\u5339\u914d\u8fd9\u4e2a\u67e5\u8be2\uff08\u7d22\u5f15\u53ef\u4ee5\u662f\u4e3b\u952e\u6216\u60df\u4e00\u7d22\u5f15\uff09\u3002\u56e0\u4e3a\u53ea\u6709\u4e00\u884c\uff0c\u8fd9\u4e2a\u503c\u5b9e\u9645\u5c31\u662f\u5e38\u6570\uff0c\u56e0\u4e3aMYSQL\u5148\u8bfb\u8fd9\u4e2a\u503c\u7136\u540e\u628a\u5b83\u5f53\u505a\u5e38\u6570\u6765\u5bf9\u5f85<\/p>\n

    eq_ref:\u5728\u8fde\u63a5\u4e2d\uff0cMYSQL\u5728\u67e5\u8be2\u65f6\uff0c\u4ece\u524d\u9762\u7684\u8868\u4e2d\uff0c\u5bf9\u6bcf\u4e00\u4e2a\u8bb0\u5f55\u7684\u8054\u5408\u90fd\u4ece\u8868\u4e2d\u8bfb\u53d6\u4e00\u4e2a\u8bb0\u5f55\uff0c\u5b83\u5728\u67e5\u8be2\u4f7f\u7528\u4e86\u7d22\u5f15\u4e3a\u4e3b\u952e\u6216\u60df\u4e00\u952e\u7684\u5168\u90e8\u65f6\u4f7f\u7528<\/p>\n

    ref:\u8fd9\u4e2a\u8fde\u63a5\u7c7b\u578b\u53ea\u6709\u5728\u67e5\u8be2\u4f7f\u7528\u4e86\u4e0d\u662f\u60df\u4e00\u6216\u4e3b\u952e\u7684\u952e\u6216\u8005\u662f\u8fd9\u4e9b\u7c7b\u578b\u7684\u90e8\u5206\uff08\u6bd4\u5982\uff0c\u5229\u7528\u6700\u5de6\u8fb9\u524d\u7f00\uff09\u65f6\u53d1\u751f\u3002\u5bf9\u4e8e\u4e4b\u524d\u7684\u8868\u7684\u6bcf\u4e00\u4e2a\u884c\u8054\u5408\uff0c\u5168\u90e8\u8bb0\u5f55\u90fd\u5c06\u4ece\u8868\u4e2d\u8bfb\u51fa\u3002\u8fd9\u4e2a\u7c7b\u578b\u4e25\u91cd\u4f9d\u8d56\u4e8e\u6839\u636e\u7d22\u5f15\u5339\u914d\u7684\u8bb0\u5f55\u591a\u5c11\u2014\u8d8a\u5c11\u8d8a\u597d<\/p>\n

    range:\u8fd9\u4e2a\u8fde\u63a5\u7c7b\u578b\u4f7f\u7528\u7d22\u5f15\u8fd4\u56de\u4e00\u4e2a\u8303\u56f4\u4e2d\u7684\u884c\uff0c\u6bd4\u5982\u4f7f\u7528>\u6216<\u67e5\u627e\u4e1c\u897f\u65f6\u53d1\u751f\u7684\u60c5\u51b5<\/p>\n

    index: \u8fd9\u4e2a\u8fde\u63a5\u7c7b\u578b\u5bf9\u524d\u9762\u7684\u8868\u4e2d\u7684\u6bcf\u4e00\u4e2a\u8bb0\u5f55\u8054\u5408\u8fdb\u884c\u5b8c\u5168\u626b\u63cf\uff08\u6bd4ALL\u66f4\u597d\uff0c\u56e0\u4e3a\u7d22\u5f15\u4e00\u822c\u5c0f\u4e8e\u8868\u6570\u636e\uff09<\/p>\n

    ALL:\u8fd9\u4e2a\u8fde\u63a5\u7c7b\u578b\u5bf9\u4e8e\u524d\u9762\u7684\u6bcf\u4e00\u4e2a\u8bb0\u5f55\u8054\u5408\u8fdb\u884c\u5b8c\u5168\u626b\u63cf\uff0c\u8fd9\u4e00\u822c\u6bd4\u8f83\u7cdf\u7cd5\uff0c\u5e94\u8be5\u5c3d\u91cf\u907f\u514d<\/p>\n

    mysql> explain select * from user where user=’root’\\G<\/p>\n

    *************************** 1. row ***************************<\/p>\n

    id: 1<\/p>\n

    select_type: SIMPLE<\/p>\n

    table: user<\/p>\n

    type: ALL<\/p>\n

    possible_keys: NULL<\/p>\n

    key: NULL<\/p>\n

    key_len: NULL<\/p>\n

    ref: NULL<\/p>\n

    rows: 5<\/p>\n

    Extra: Using where<\/p>\n

    1 row in set (0.00 sec)<\/p>\n","protected":false},"excerpt":{"rendered":"

    explain\u663e\u793a\u4e86mysql\u5982\u4f55\u4f7f\u7528\u7d22\u5f15\u6765\u5904\u7406select\u8bed\u53e5\u4ee5\u53ca\u8fde\u63a5\u8868\u3002\u53ef\u4ee5\u5e2e\u52a9\u9009\u62e9\u66f4\u597d\u7684\u7d22\u5f15\u548c\u5199\u51fa\u66f4\u4f18\u5316 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[21],"tags":[27],"class_list":["post-887","post","type-post","status-publish","format-standard","hentry","category-mysql","tag-mysql"],"_links":{"self":[{"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/posts\/887","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=887"}],"version-history":[{"count":1,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/posts\/887\/revisions"}],"predecessor-version":[{"id":889,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=\/wp\/v2\/posts\/887\/revisions\/889"}],"wp:attachment":[{"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=887"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=887"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.royalwzy.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=887"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}