{"id":181272,"date":"2024-11-09T15:40:16","date_gmt":"2024-11-09T07:40:16","guid":{"rendered":"https:\/\/server.hk\/cnblog\/181272\/"},"modified":"2024-11-09T15:40:17","modified_gmt":"2024-11-09T07:40:17","slug":"%e6%b7%b1%e5%85%a5%e7%90%86%e8%a7%a3%e6%95%b8%e6%93%9a%e5%ba%ableft-join%e5%8e%9f%e7%90%86%ef%bc%8c%e5%84%aa%e5%8c%96%e6%9f%a5%e8%a9%a2%e6%95%88%e7%8e%87%ef%bc%88%e6%95%b8%e6%93%9a%e5%ba%ableft-join","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/181272\/","title":{"rendered":"\u6df1\u5165\u7406\u89e3\u6578\u64da\u5eableft join\u539f\u7406\uff0c\u512a\u5316\u67e5\u8a62\u6548\u7387\uff08\u6578\u64da\u5eableft join\u539f\u7406\uff09"},"content":{"rendered":"<h1 id=\"%e6%b7%b1%e5%85%a5%e7%90%86%e8%a7%a3%e6%95%b8%e6%93%9a%e5%ba%ableft-join%e5%8e%9f%e7%90%86%ef%bc%8c%e5%84%aa%e5%8c%96%e6%9f%a5%e8%a9%a2%e6%95%88%e7%8e%87-wVrUnialFq\">\u6df1\u5165\u7406\u89e3\u6578\u64da\u5eabLEFT 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JOIN\u901a\u5e38\u7528\u65bc\u4ee5\u4e0b\u5e7e\u7a2e\u60c5\u6cc1\uff1a<\/p>\n<ul>\n<li><strong>\u9700\u8981\u4fdd\u7559\u5de6\u5074\u8868\u7684\u6240\u6709\u6578\u64da\uff1a<\/strong>\u7576\u6211\u5011\u5e0c\u671b\u7372\u53d6\u5de6\u5074\u8868\u7684\u6240\u6709\u8a18\u9304\uff0c\u5373\u4f7f\u53f3\u5074\u8868\u4e2d\u6c92\u6709\u5c0d\u61c9\u7684\u6578\u64da\u6642\uff0cLEFT JOIN\u662f\u6700\u4f73\u9078\u64c7\u3002<\/li>\n<li><strong>\u6578\u64da\u5b8c\u6574\u6027\uff1a<\/strong>\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u5de6\u5074\u8868\u7684\u6578\u64da\u53ef\u80fd\u662f\u95dc\u9375\u7684\uff0c\u800c\u53f3\u5074\u8868\u7684\u6578\u64da\u5247\u662f\u8f14\u52a9\u7684\uff0c\u9019\u6642\u4f7f\u7528LEFT JOIN\u53ef\u4ee5\u78ba\u4fdd\u4e0d\u4e1f\u5931\u4efb\u4f55\u91cd\u8981\u4fe1\u606f\u3002<\/li>\n<li><strong>\u5831\u544a\u751f\u6210\uff1a<\/strong>\u5728\u751f\u6210\u5831\u544a\u6642\uff0c\u53ef\u80fd\u9700\u8981\u986f\u793a\u6240\u6709\u7684\u5ba2\u6236\uff0c\u5373\u4f7f\u67d0\u4e9b\u5ba2\u6236\u6c92\u6709\u8a02\u55ae\u8a18\u9304\uff0c\u9019\u6642\u4f7f\u7528LEFT JOIN\u53ef\u4ee5\u9054\u5230\u76ee\u7684\u3002<\/li>\n<\/ul>\n<h2 id=\"%e5%84%aa%e5%8c%96left-join%e6%9f%a5%e8%a9%a2%e6%95%88%e7%8e%87%e7%9a%84%e7%ad%96%e7%95%a5-wVrUnialFq\">\u512a\u5316LEFT JOIN\u67e5\u8a62\u6548\u7387\u7684\u7b56\u7565<\/h2>\n<p>\u5118\u7ba1LEFT JOIN\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\u975e\u5e38\u6709\u7528\uff0c\u4f46\u4e0d\u7576\u4f7f\u7528\u53ef\u80fd\u6703\u5c0e\u81f4\u67e5\u8a62\u6548\u7387\u4f4e\u4e0b\u3002\u4ee5\u4e0b\u662f\u4e00\u4e9b\u512a\u5316LEFT JOIN\u67e5\u8a62\u6548\u7387\u7684\u7b56\u7565\uff1a<\/p>\n<h3 id=\"1-%e4%bd%bf%e7%94%a8%e7%b4%a2%e5%bc%95-wVrUnialFq\">1. \u4f7f\u7528\u7d22\u5f15<\/h3>\n<p>\u5728JOIN\u64cd\u4f5c\u4e2d\uff0c\u7d22\u5f15\u53ef\u4ee5\u986f\u8457\u63d0\u9ad8\u67e5\u8a62\u6027\u80fd\u3002\u78ba\u4fdd\u5728JOIN\u689d\u4ef6\u4e2d\u4f7f\u7528\u7684\u5b57\u6bb5\u4e0a\u5275\u5efa\u7d22\u5f15\uff0c\u9019\u6a23\u6578\u64da\u5eab\u53ef\u4ee5\u66f4\u5feb\u5730\u67e5\u627e\u5339\u914d\u7684\u8a18\u9304\u3002<\/p>\n<pre><code>CREATE INDEX idx_a_id ON TableB(a_id);<\/code><\/pre>\n<h3 id=\"2-%e9%81%bf%e5%85%8d%e4%b8%8d%e5%bf%85%e8%a6%81%e7%9a%84%e5%ad%97%e6%ae%b5%e9%81%b8%e6%93%87-wVrUnialFq\">2. \u907f\u514d\u4e0d\u5fc5\u8981\u7684\u5b57\u6bb5\u9078\u64c7<\/h3>\n<p>\u5728SELECT\u8a9e\u53e5\u4e2d\uff0c\u53ea\u9078\u64c7\u9700\u8981\u7684\u5b57\u6bb5\uff0c\u800c\u4e0d\u662f\u4f7f\u7528\u201c*\u201d\u4f86\u9078\u64c7\u6240\u6709\u5b57\u6bb5\u3002\u9019\u6a23\u53ef\u4ee5\u6e1b\u5c11\u6578\u64da\u50b3\u8f38\u91cf\uff0c\u63d0\u9ad8\u67e5\u8a62\u6548\u7387\u3002<\/p>\n<pre><code>SELECT A.name, B.order_date\nFROM TableA A\nLEFT JOIN TableB B ON A.id = B.a_id;<\/code><\/pre>\n<h3 id=\"3-%e9%99%90%e5%88%b6%e7%b5%90%e6%9e%9c%e9%9b%86-wVrUnialFq\">3. \u9650\u5236\u7d50\u679c\u96c6<\/h3>\n<p>\u4f7f\u7528WHERE\u5b50\u53e5\u4f86\u9650\u5236\u7d50\u679c\u96c6\u7684\u5927\u5c0f\uff0c\u9019\u6a23\u53ef\u4ee5\u6e1b\u5c11\u6578\u64da\u5eab\u7684\u8ca0\u64d4\uff0c\u5f9e\u800c\u63d0\u9ad8\u67e5\u8a62\u901f\u5ea6\u3002<\/p>\n<pre><code>SELECT A.*, B.*\nFROM TableA A\nLEFT JOIN TableB B ON A.id = B.a_id\nWHERE A.status = 'active';<\/code><\/pre>\n<h3 id=\"4-%e8%80%83%e6%85%ae%e4%bd%bf%e7%94%a8inner-join-wVrUnialFq\">4. \u8003\u616e\u4f7f\u7528INNER JOIN<\/h3>\n<p>\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u5982\u679c\u4e0d\u9700\u8981\u4fdd\u7559\u5de6\u5074\u8868\u7684\u6240\u6709\u8a18\u9304\uff0c\u53ef\u4ee5\u8003\u616e\u4f7f\u7528INNER JOIN\uff0c\u9019\u6a23\u53ef\u4ee5\u63d0\u9ad8\u67e5\u8a62\u6548\u7387\uff0c\u56e0\u70baINNER JOIN\u53ea\u8fd4\u56de\u5169\u500b\u8868\u4e2d\u90fd\u6709\u7684\u8a18\u9304\u3002<\/p>\n<h2 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