{"id":200418,"date":"2025-05-06T13:04:37","date_gmt":"2025-05-06T05:04:37","guid":{"rendered":"https:\/\/server.hk\/cnblog\/200418\/"},"modified":"2025-05-06T13:04:37","modified_gmt":"2025-05-06T05:04:37","slug":"%e5%a6%82%e4%bd%95%e4%bc%98%e5%8c%96%e5%a4%a7%e5%9e%8b%e6%95%b0%e6%8d%ae%e5%ba%93%e7%b3%bb%e7%bb%9f%e4%b8%ad%e4%b8%a4%e4%b8%aa%e6%97%a0%e5%85%b3%e8%81%94%e8%a1%a8%e7%9a%84%e7%ac%9b%e5%8d%a1%e5%b0%94","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/200418\/","title":{"rendered":"\u5982\u4f55\u4f18\u5316\u5927\u578b\u6570\u636e\u5e93\u7cfb\u7edf\u4e2d\u4e24\u4e2a\u65e0\u5173\u8054\u8868\u7684\u7b1b\u5361\u5c14\u79ef\u67e5\u8be2\uff1f"},"content":{"rendered":"<p><b><\/b> 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class=\"aligncenter\"><\/p>\n<p><strong>\u6570\u636e\u5e93\u67e5\u8be2\u6548\u7387\u4f18\u5316<\/strong><\/p>\n<p>\u5728\u5927\u578b\u6570\u636e\u5e93\u7cfb\u7edf\u4e2d\uff0c\u67e5\u8be2\u6548\u7387\u5c24\u4e3a\u91cd\u8981\u3002\u672c\u6587\u5c06\u9488\u5bf9\u4e24\u4e2a\u65e0\u5173\u8054\u8868\u7684\u7b1b\u5361\u5c14\u79ef\u95ee\u9898\u63d0\u51fa\u89e3\u51b3\u65b9\u6848\uff0c\u5e76\u6839\u636e\u5b9e\u9645\u573a\u666f\u7ed9\u51fa\u4f18\u5316\u67e5\u8be2\u8bed\u53e5\u7684\u5efa\u8bae\u3002<\/p>\n<p><strong>\u7b1b\u5361\u5c14\u79ef\u95ee\u9898<\/strong><\/p>\n<p>\u5f53\u67e5\u8be2\u6d89\u53ca\u4e24\u4e2a\u65e0\u5173\u8054\u8868\u65f6\uff0c\u82e5\u6ca1\u6709\u4efb\u4f55\u7b5b\u9009\u6761\u4ef6\uff0c\u5c06\u4f1a\u4ea7\u751f\u7b1b\u5361\u5c14\u79ef\uff0c\u5bfc\u81f4\u7ed3\u679c\u96c6\u6570\u91cf\u5448\u51e0\u4f55\u500d\u6570\u589e\u957f\u3002\u4f8b\u5982\uff0c\u82e5\u8868 a \u6709 4 \u884c\uff0c\u8868 b \u6709 2 \u884c\uff0c\u65e0\u6761\u4ef6\u67e5\u8be2\u7684\u7ed3\u679c\u5c06\u4ea7\u751f 4 x 2 = 8 \u6761\u6570\u636e\u3002<\/p>\n<p><strong>\u4f18\u5316\u67e5\u8be2\u8bed\u53e5<\/strong><\/p>\n<p>\u82e5\u5b58\u5728\u7b2c\u4e09\u5f20\u8868 c \u4e0e\u8868 a \u548c b \u76f8\u5173\u8054\uff0c\u53ef\u91c7\u7528\u4ee5\u4e0b\u65b9\u6cd5\u4f18\u5316\u67e5\u8be2\u8bed\u53e5\uff1a<\/p>\n<ul>\n<li>\u4ee5\u6570\u636e\u8f83\u591a\u7684\u8868\u4f5c\u4e3a\u4e3b\u8868\uff0c\u5982\u8868 a\u3002<\/li>\n<li>\u4f7f\u7528 left join \u8bed\u53e5\u5173\u8054\u8868 c \u548c a\uff0c\u6309\u59d3\u540d\u7b5b\u9009\u3002<\/li>\n<li>\u518d\u4f7f\u7528 left join \u8bed\u53e5\u5173\u8054\u8868 b \u548c\u67e5\u8be2\u7ed3\u679c\uff0c\u6309\u7701\u4efd\u7b5b\u9009\u3002<\/li>\n<\/ul>\n<p>\u4f18\u5316\u540e\u7684\u67e5\u8be2\u8bed\u53e5\u5982\u4e0b\uff1a<\/p>\n<pre>SELECT A.*, B.*\nFROM C\n  LEFT JOIN A ON C.nid = A.id\n  LEFT JOIN B ON C.sid = B.id\nWHERE A.name = '\u5f20\u4e09' AND B.\u7701\u4efd = '\u4e0a\u6d77'<\/pre>\n<p>\u6b64\u67e5\u8be2\u8bed\u53e5\u5229\u7528\u8868\u4e4b\u95f4\u7684\u5173\u8054\u5173\u7cfb\uff0c\u907f\u514d\u4e86\u7b1b\u5361\u5c14\u79ef\u3002<\/p>\n<p><strong>\u5176\u4ed6\u5efa\u8bae<\/strong><\/p>\n<p>\u6b64\u5916\uff0c\u4ee5\u4e0b\u5efa\u8bae\u4e5f\u6709\u52a9\u4e8e\u8fdb\u4e00\u6b65\u4f18\u5316\u67e5\u8be2\u6548\u7387\uff1a<\/p>\n<ul>\n<li>\u521b\u5efa\u9002\u5f53\u7684\u7d22\u5f15\u3002<\/li>\n<li>\u4f7f\u7528 explain 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