{"id":2150,"date":"2020-06-29T21:50:50","date_gmt":"2020-06-29T13:50:50","guid":{"rendered":"http:\/\/47.101.202.111\/?p=2150"},"modified":"2023-04-04T17:23:20","modified_gmt":"2023-04-04T09:23:20","slug":"db-optimized","status":"publish","type":"post","link":"http:\/\/139.196.114.170\/?p=2150","title":{"rendered":"SQL\u6027\u80fd\u4f18\u5316 – JOIN\u5b9e\u73b0\u539f\u7406\u53ca\u4f18\u5316\u601d\u8def"},"content":{"rendered":"

JOIN\u5b9e\u73b0\u539f\u7406\u4e0e\u4f18\u5316<\/h2>\n

\u5b9e\u73b0\u539f\u7406<\/h3>\n

\u5047\u8bbeA\u8868 \\scriptsize N_a<\/code> \u884c\uff0cB\u8868 \\scriptsize N_b<\/code> \u884c<\/p>\n

SELECT * FROM A\nLEFT JOIN B\nON A.id = B.refId<\/code><\/pre>\n
Simple Nested-Loop Join<\/h4>\n
\u8fde\u63a5\u7b97\u6cd5\u7684\u57fa\u672c\u601d\u60f3\u662f\u5148\u505a\u7b1b\u5361\u5c14\u79ef\u518d\u8fdb\u884c\u7b5b\u9009\uff0c\u6700\u7b80\u5355\u7684\u5b9e\u73b0\u662f\u53cc\u91cd\u5faa\u73af\uff1a\u5916\u5c42\u5faa\u73af\u56fa\u5b9a\u5de6\u8868\u884c\uff0c\u5185\u5b58\u5faa\u73af\u904d\u5386\u548c\u5339\u914d\u53f3\u8868\u884c\uff0c\u6bcf\u5339\u914d\u6210\u529f\u5f62\u6210\u4e00\u4e2a\u7ed3\u679c\u884c\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 \\scriptsize O(N_aN_b)<\/code><\/p>\n
Block Nested-Loop Join<\/h4>\n
Simple Nested-Loop Join\u662f\u6b64\u7b97\u6cd5\u7684\u903b\u8f91\u539f\u7406\uff0c\u8fde\u63a5\u5339\u914d\u65b9\u5f0f\u5747\u76f8\u540c\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 \\scriptsize O(N_aN_b)<\/code>\u3002\u4f46\u5728\u7cfb\u7edf\u5b9e\u73b0\u65f6\u6570\u636e\u4ee5\u5185\u5b58\u5757\u7684\u5f62\u5f0f\u4ece\u78c1\u76d8\u52a0\u8f7d\u5230\u5185\u5b58\uff0c\u8fd9\u6837\u5c31\u51cf\u5c11\u4e86IO\u6b21\u6570\uff0c\u4ece\u800c\u63d0\u5347\u8fde\u63a5\u901f\u5ea6<\/p>\n
Index Nested-Loop Join<\/h4>\n
\u8fde\u63a5\u7684\u5de6\u8868\u5fc5\u987b\u5b8c\u6574\u626b\u63cf\uff0c\u4f46\u5728\u53f3\u8868\u4e2d\u5339\u914d\u5de6\u8868\u5173\u8054\u952e\u65f6\uff0c\u65e0\u9700\u904d\u5386\u6574\u5f20\u53f3\u8868\uff0c\u53ef\u7528\u67e5\u627e\u7b97\u6cd5\u4f18\u5316\u5173\u8054\u952e\u503c\u7684\u67e5\u8be2\u6027\u80fd<\/p>\n
\u5f53\u53f3\u8868\u4f7f\u7528B+\u6811\u7d22\u5f15\u65f6\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 \\scriptsize O(N_alogN_b)<\/code>
\n\u5f53\u53f3\u8868\u4f7f\u7528Hash\u7d22\u5f15\u65f6\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 \\scriptsize O(N_a)<\/code><\/p>\n
\u4f18\u5316\u601d\u8def<\/h2>\n
\u51cf\u5c11\u8fde\u8868\uff1a\u4ece\u4e1a\u52a1\u548c\u8868\u8bbe\u8ba1\u4e0a\u7b80\u5316<\/h3>\n
\u4e00\u822c\u60c5\u51b5\u4e0b\u4e0d\u8d85\u8fc73\u5f20\u8868\u8fde\u63a5\uff0c\u5426\u5219\u4f7f\u7528\u5197\u4f59\u5217\uff0c\u7528\u7a7a\u95f4\u6362\u65f6\u95f4<\/p>\n
\u67e5\u8be2\u6548\u7387\uff1a\u51cf\u5c11\u626b\u63cf\u884c\u6570<\/h3>\n
\u5f3a\u5236\u4fee\u6539\u9a71\u52a8\u8868<\/h4>\n
\u5de6\u8868\u88ab\u79f0\u4e3a\u9a71\u52a8\u8868\u3002\u4f9d\u636eIndex Nested-Loop Join\u4e2d\u7684\u5206\u6790\uff0c\u4f7f\u7528\u7d22\u5f15\u65f6\uff0c\u65f6\u95f4\u590d\u6742\u5ea6\u4e3b\u8981\u53d6\u51b3\u4e8e \\scriptsize N_a<\/code>\uff0c\u56e0\u6b64\u9009\u62e9\u884c\u6570\u6bd4\u8f83\u5c0f\u7684\u8868\u4f5c\u4e3a\u5de6\u8868\u53ef\u63d0\u5347\u6027\u80fd<\/p>\n
\u4e3a\u4e86\u9632\u6b62\u4f18\u5316\u5668\u66f4\u6539\u9a71\u52a8\u8868\uff0c\u4f7f\u7528straight join<\/code><\/code>\u53ef\u5f3a\u5236\u4f7f\u5f97\u5de6\u8868\u6210\u4e3a\u9a71\u52a8\u8868<\/p>\n
\u4f7f\u7528B+\u7d22\u5f15<\/h4>\n
\u5de6\u8868\u7684\u7d22\u5f15\u4e3b\u8981\u7528\u4e8eWHERE\u8bed\u53e5\u7b5b\u9009\u51fa\u9a71\u52a8\u8868
\n\u53f3\u8868\u7684\u7d22\u5f15\u7528\u4e8e\u5173\u8054\u952e\u503c\u67e5\u8be2\u964d\u4f4e\u8fde\u63a5\u6210\u672c<\/p>\n
\u53f3\u8868\u4f7f\u7528B+\u6811\u7d22\u5f15\u8fde\u63a5\u65f6\uff0c\u8fde\u63a5\u590d\u6742\u5ea6\u964d\u4e3a \\scriptsize O(N_a + N_alogN_b)<\/code><\/p>\n
\u4f7f\u7528Hash\u7d22\u5f15<\/h4>\n
\u53f3\u8868\u4f7f\u7528Hash\u7d22\u5f15\u8fde\u63a5\u65f6\uff0c\u8fde\u63a5\u590d\u6742\u5ea6\u964d\u4e3a \\scriptsize O(N_a)<\/code><\/p>\n
\u6570\u636e\u5e93\u5c42\u9762\u5b9e\u73b0\uff1aMySQL\u57288.0.20\u4e4b\u540e\u652f\u6301Hash\u7d22\u5f15
\n\u4e1a\u52a1\u5c42\u9762\u5b9e\u73b0\uff1a\u53ef\u4ee5\u5148\u5c06\u5de6\u53f3\u8868\u6570\u636e\u624b\u52a8\u67e5\u51fa\uff0c\u6784\u9020\u5173\u8054\u952eset\uff0c\u9010\u4e00\u8fde\u63a5\u62fc\u88c5\u7ed3\u679c\u96c6<\/p>\n
\u63d0\u5347IO\u6548\u7387<\/h3>\n
\u8c03\u5927\u8fde\u63a5\u7f13\u5b58<\/h4>\n
\u5185\u5b58\u53ef\u88c5\u4e0b\u7684\u6570\u636e\u91cf\u8d8a\u591a\uff0cIO\u6b21\u6570\u8d8a\u5c11\uff0c\u6027\u80fd\u4e5f\u66f4\u9ad8\u3002\u56e0\u6b64\u589e\u52a0\u8fde\u63a5\u64cd\u4f5c\u4e2d\u5206\u914d\u7684\u4e34\u65f6\u5185\u5b58\u53ef\u4f18\u5316\u8fde\u63a5\u6027\u80fd\uff0c\u8fde\u63a5\u7ed3\u675f\u540e\u4e34\u65f6\u5185\u5b58\u88ab\u56de\u6536\u3002\u53ef\u901a\u8fc7 join buffer<\/code><\/code> \u6765\u8c03\u8282\u5355\u4e2asession\u7684join\u7f13\u5b58\u5927\u5c0f<\/p>\n
\u8f6c\u6362\u987a\u5e8fIO<\/h4>\n
\u6309\u7167\u5de6\u8868\u6570\u636e\u884c\u987a\u5e8f\uff0c\u6839\u636e\u5173\u8054\u952e\u7d22\u5f15\u56de\u8868\u5b9a\u4f4d\u5230\u53f3\u8868\u6570\u636e\u884c\u8fdb\u884c\u8fde\u63a5\uff0c\u6b64\u65f6\u5bf9\u53f3\u8868\u6570\u636e\u7684\u8bfb\u53d6\u662f\u968f\u673aIO\u3002\u5982\u679c\u79ef\u6512\u4e00\u5b9a\u6570\u91cf\u7684\u56de\u8868\u540e\u7684\u53f3\u8868\u4e3b\u952e\uff0c\u5c06\u4e3b\u952e\u6392\u5e8f\u540e\u518d\u8fdb\u884c\u8bfb\u53d6\u8fde\u63a5\uff0c\u5c06\u8fdb\u4e00\u6b65\u51cf\u5c11IO\u6b21\u6570\uff0c\u8fd9\u4e2a\u987a\u5e8f\u8bfb\u673a\u5236\u88ab\u79f0\u4e3a Multi-Range Read<\/strong>\uff0c\u7528\u5728JOIN\u573a\u666f\u4e2d\u79f0\u4e3a Batched Key Access<\/strong><\/p>\n
\u901a\u8fc7\u4ee5\u4e0b\u53c2\u6570\u5f00\u542f<\/p>\n
set optimizer_switch='mrr=on,mrr_cost_based=off,batched_key_access=on'<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
JOIN\u5b9e\u73b0\u539f\u7406\u4e0e\u4f18\u5316 \u5b9e\u73b0\u539f\u7406 \u5047\u8bbeA\u8868 \\scriptsize N_a \u884c\uff0cB\u8868 \\scriptsize  … <\/p>\n
\u7ee7\u7eed\u9605\u8bfb\u201cSQL\u6027\u80fd\u4f18\u5316 – JOIN\u5b9e\u73b0\u539f\u7406\u53ca\u4f18\u5316\u601d\u8def\u201d<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[40],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/2150"}],"collection":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2150"}],"version-history":[{"count":4,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/2150\/revisions"}],"predecessor-version":[{"id":2720,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/2150\/revisions\/2720"}],"wp:attachment":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2150"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2150"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2150"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}