{"id":7072,"date":"2024-11-14T13:44:09","date_gmt":"2024-11-14T05:44:09","guid":{"rendered":"https:\/\/fwq.ai\/blog\/7072\/"},"modified":"2024-11-14T13:44:09","modified_gmt":"2024-11-14T05:44:09","slug":"%e5%a6%82%e4%bd%95%e5%a4%84%e7%90%86%e8%81%94%e5%90%88%e6%9f%a5%e8%af%a2%e4%b8%ad%e7%bc%ba%e5%a4%b1%e7%9a%84%e5%85%b3%e8%81%94%e8%ae%b0%e5%bd%95%e5%b9%b6%e4%bf%9d%e7%95%99%e6%89%80%e6%9c%89%e7%ad%96","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/7072\/","title":{"rendered":"\u5982\u4f55\u5904\u7406\u8054\u5408\u67e5\u8be2\u4e2d\u7f3a\u5931\u7684\u5173\u8054\u8bb0\u5f55\u5e76\u4fdd\u7559\u6240\u6709\u7b56\u7565\u4fe1\u606f\uff1f"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/001\/246\/273\/173038442254501.jpg\" class=\"aligncenter\" title=\"\u5982\u4f55\u5904\u7406\u8054\u5408\u67e5\u8be2\u4e2d\u7f3a\u5931\u7684\u5173\u8054\u8bb0\u5f55\u5e76\u4fdd\u7559\u6240\u6709\u7b56\u7565\u4fe1\u606f\uff1f\u63d2\u56fe\" 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join\u64cd\u4f5c\u3002left join\u4f1a\u4fdd\u7559\u5de6\u8868\uff08strategy\u8868\uff09\u7684\u6240\u6709\u8bb0\u5f55\uff0c\u5373\u4f7f\u5728\u53f3\u8868\uff08group\u8868\uff09\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002\u6b64\u5916\uff0cleft join\u8fd8\u53ef\u4ee5\u4f7f\u7528if\u51fd\u6570\u8bbe\u7f6e\u4e00\u4e2a\u9ed8\u8ba4\u503c\uff0c\u5f53gatewaymac\u5b57\u6bb5\u4e3a\u7a7a\u65f6\uff0c\u663e\u793a\u8fd9\u4e2a\u9ed8\u8ba4\u503c\u3002<\/p>\n<p><strong>\uff1a<\/strong><\/p>\n<pre>SELECT strategy.*, IF(gatewaymac IS NULL, 'defaultValue', gatewaymac) AS gatewaymac\nFROM strategy\nLEFT JOIN strategy_group ON strategy.id = strategy_group.strategy_id\nLEFT JOIN group ON strategy_group.group_id = group.id<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u901a\u8fc7\u4f7f\u7528left join\u64cd\u4f5c\u548cif\u51fd\u6570\uff0c\u53ef\u4ee5\u786e\u4fdd\u67e5\u8be2\u7ed3\u679c\u4e2d\u5305\u542b\u6240\u6709strategy\u8bb0\u5f55\uff0c\u5373\u4f7f\u8fd9\u4e9b\u8bb0\u5f55\u5728group\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002gatewaymac\u5b57\u6bb5\u4e3a\u7a7a\u65f6\uff0c\u5c06\u663e\u793a\u6307\u5b9a\u7684\u9ed8\u8ba4\u503c\u3002<\/p>\n<p>\u4ee5\u4e0a\u5c31\u662f\u5982\u4f55\u5904\u7406\u8054\u5408\u67e5\u8be2\u4e2d\u7f3a\u5931\u7684\u5173\u8054\u8bb0\u5f55\u5e76\u4fdd\u7559\u6240\u6709\u7b56\u7565\u4fe1\u606f\uff1f\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u7f51\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5904\u7406\u8054\u5408\u67e5\u8be2\u4e2d\u7684\u7f3a\u5931\u503c \u5728\u6570\u636e\u5e93\u67e5\u8be2\u4e2d\uff0c\u7ecf\u5e38\u9700\u8981\u5bf9\u591a\u4e2a\u8868\u8fdb\u884c\u8054\u5408\u67e5\u8be2\u3002\u4f46\u662f\uff0c\u5f53\u6d89\u53ca\u5230\u5173\u8054\u8868\u65f6\uff0c\u53ef\u80fd\u5b58\u5728\u4e00\u4e9b\u8bb0\u5f55\u5728\u5173\u8054\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002\u6b64\u65f6\uff0c\u67e5\u8be2\u7ed3\u679c\u5c31\u4f1a\u7f3a\u5931\u8fd9\u4e9b\u8bb0\u5f55\uff0c\u8fd9\u53ef\u80fd\u4f1a\u5f71\u54cd\u67e5\u8be2\u7684\u51c6\u786e\u6027\u3002 \u95ee\u9898\uff1a \u6709\u4e09\u4e2a\u8868\uff1astrategy\u3001group\u548cstrategy_group\u3002\u5176\u4e2d\uff0cstrategy_group\u8868\u662fstrategy\u8868\u548cgroup\u8868\u7684\u8054\u7cfb\u5bf9\u5e94\u8868\u3002\u9700\u8981\u67e5\u8be2strategy\u8868\u7684\u6240\u6709\u8bb0\u5f55\uff0c\u5e76\u540c\u65f6\u83b7\u53d6group\u8868\u4e2d\u7684gatewaymac\u5b57\u6bb5\u3002\u4f46\u662f\uff0c\u73b0\u5728\u7684\u95ee\u9898\u662f\uff0c\u5bf9\u4e8e\u90a3\u4e9b\u5728strategy_group\u8868\u4e2d\u6ca1\u6709\u5173\u8054\u7684strategy\u8bb0\u5f55\uff0c\u67e5\u8be2\u7ed3\u679c\u4e2d\u4f1a\u7f3a\u5931\u3002 \u89e3\u51b3\u65b9\u6848\uff1a \u4e3a\u4e86\u4fdd\u7559\u8fd9\u4e9b\u6ca1\u6709\u5173\u8054\u7684strategy\u8bb0\u5f55\uff0c\u9700\u8981\u4f7f\u7528left join\u64cd\u4f5c\u3002left join\u4f1a\u4fdd\u7559\u5de6\u8868\uff08strategy\u8868\uff09\u7684\u6240\u6709\u8bb0\u5f55\uff0c\u5373\u4f7f\u5728\u53f3\u8868\uff08group\u8868\uff09\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002\u6b64\u5916\uff0cleft join\u8fd8\u53ef\u4ee5\u4f7f\u7528if\u51fd\u6570\u8bbe\u7f6e\u4e00\u4e2a\u9ed8\u8ba4\u503c\uff0c\u5f53gatewaymac\u5b57\u6bb5\u4e3a\u7a7a\u65f6\uff0c\u663e\u793a\u8fd9\u4e2a\u9ed8\u8ba4\u503c\u3002 \uff1a SELECT strategy.*, IF(gatewaymac IS NULL, &#8216;defaultValue&#8217;, gatewaymac) AS gatewaymac FROM strategy LEFT JOIN strategy_group ON strategy.id = strategy_group.strategy_id LEFT JOIN group ON strategy_group.group_id = group.id \u767b\u5f55\u540e\u590d\u5236 \u901a\u8fc7\u4f7f\u7528left join\u64cd\u4f5c\u548cif\u51fd\u6570\uff0c\u53ef\u4ee5\u786e\u4fdd\u67e5\u8be2\u7ed3\u679c\u4e2d\u5305\u542b\u6240\u6709strategy\u8bb0\u5f55\uff0c\u5373\u4f7f\u8fd9\u4e9b\u8bb0\u5f55\u5728group\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u8bb0\u5f55\u3002gatewaymac\u5b57\u6bb5\u4e3a\u7a7a\u65f6\uff0c\u5c06\u663e\u793a\u6307\u5b9a\u7684\u9ed8\u8ba4\u503c\u3002 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