{"id":200379,"date":"2025-05-06T10:33:00","date_gmt":"2025-05-06T02:33:00","guid":{"rendered":"https:\/\/server.hk\/cnblog\/200379\/"},"modified":"2025-05-06T10:33:00","modified_gmt":"2025-05-06T02:33:00","slug":"%e6%95%b0%e6%8d%ae%e5%ba%93%e5%85%b3%e8%81%94%e6%9f%a5%e8%af%a2%e4%b8%ad%e5%a6%82%e4%bd%95%e5%b0%86%e7%a9%ba%e5%80%bc%e8%ae%be%e7%bd%ae%e4%b8%ba%e9%bb%98%e8%ae%a4%e5%80%bc%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/200379\/","title":{"rendered":"\u6570\u636e\u5e93\u5173\u8054\u67e5\u8be2\u4e2d\u5982\u4f55\u5c06\u7a7a\u503c\u8bbe\u7f6e\u4e3a\u9ed8\u8ba4\u503c\uff1f"},"content":{"rendered":"<p><b><\/b> <\/p>\n<h1>\u6570\u636e\u5e93\u5173\u8054\u67e5\u8be2\u4e2d\u5982\u4f55\u5c06\u7a7a\u503c\u8bbe\u7f6e\u4e3a\u9ed8\u8ba4\u503c\uff1f<\/h1>\n<p>\u5927\u5bb6\u597d\uff0c\u6211\u4eec\u53c8\u89c1\u9762\u4e86\u554a~\u672c\u6587\u7684\u5185\u5bb9\u4e2d\u5c06\u4f1a\u6d89\u53ca\u5230\u7b49\u7b49\u3002\u5982\u679c\u4f60\u6b63\u5728\u5b66\u4e60\u76f8\u5173\u77e5\u8bc6\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\uff0c\u4ee5\u540e\u4f1a\u7ed9\u5927\u5bb6\u5e26\u6765\u66f4\u591a\u76f8\u5173\u6587\u7ae0\uff0c\u5e0c\u671b\u6211\u4eec\u80fd\u4e00\u8d77\u8fdb\u6b65\uff01\u4e0b\u9762\u5c31\u5f00\u59cb\u672c\u6587\u7684\u6b63\u5f0f\u5185\u5bb9~<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20241103\/1730630392672752f86b8dc.jpg\" class=\"aligncenter\"><\/p>\n<p><strong>\u6570\u636e\u5e93\u5173\u8054\u67e5\u8be2\uff1a\u5c06\u7a7a\u503c\u8bbe\u7f6e\u4e3a\u9ed8\u8ba4\u503c<\/strong><\/p>\n<p>\u5728\u6570\u636e\u5e93\u5904\u7406\u4e2d\uff0c\u6211\u4eec\u7ecf\u5e38\u9700\u8981\u4f7f\u7528\u5173\u8054\u67e5\u8be2\u6765\u4ece\u591a\u4e2a\u8868\u4e2d\u83b7\u53d6\u6570\u636e\u3002\u4f46\u662f\uff0c\u5f53\u6709\u4e00\u4e2a\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u6570\u636e\u65f6\uff0c\u67e5\u8be2\u7ed3\u679c\u4e2d\u4f1a\u663e\u793a\u4e3a null \u503c\u3002\u5bf9\u4e8e\u67d0\u4e9b\u573a\u666f\uff0c\u6211\u4eec\u9700\u8981\u5c06\u8fd9\u4e9b null \u503c\u8bbe\u7f6e\u4e3a\u4e00\u4e2a\u7279\u5b9a\u7684\u9ed8\u8ba4\u503c\u3002<\/p>\n<p>\u4ee5\u4e0b\u662f\u5982\u4f55\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\u7684\u6b65\u9aa4\uff1a<\/p>\n<p><strong>1. \u4f7f\u7528 left join<\/strong><\/p>\n<p>left join \u64cd\u4f5c\u7b26\u7528\u4e8e\u5728\u5916\u8fde\u63a5\u4e2d\u4fdd\u7559\u88ab\u8fde\u63a5\u8868\u4e2d\u7684\u6240\u6709\u884c\uff0c\u5373\u4f7f\u5176\u4e2d\u4e00\u4e9b\u884c\u6ca1\u6709\u4e0e\u4e3b\u8868\u76f8\u5339\u914d\u3002\u5728\u8fd9\u4e2a\u60c5\u51b5\u4e0b\uff0cleft join \u5c06\u4fdd\u7559\u6240\u6709 strategy \u8868\u4e2d\u7684\u884c\uff0c\u5373\u4f7f\u5b83\u4eec\u6ca1\u6709\u4e0e group \u8868\u4e2d\u5b58\u5728\u5bf9\u5e94\u7684 strategy_group\u3002<\/p>\n<p><strong>2. \u4f7f\u7528 if \u51fd\u6570<\/strong><\/p>\n<p>if \u51fd\u6570\u5141\u8bb8\u6211\u4eec\u57fa\u4e8e\u6761\u4ef6\u8fd4\u56de\u4e0d\u540c\u7684\u503c\u3002\u5728\u672c\u4f8b\u4e2d\uff0c\u6211\u4eec\u4f7f\u7528 if \u51fd\u6570\u6765\u68c0\u67e5 gatewaymac \u5b57\u6bb5\u662f\u5426\u4e3a null\u3002\u5982\u679c\u662f\uff0c\u5219\u8fd4\u56de\u9ed8\u8ba4\u503c\uff0c\u5426\u5219\u8fd4\u56de gatewaymac \u5b57\u6bb5\u7684\u503c\u3002<\/p>\n<pre>SELECT strategy.*, IF(gatewaymac IS NULL, 'defaultValue', gatewaymac) AS gatewaymac\nFROM strategy\nLEFT JOIN group ON strategy.id = strategy_group.strategy_id\nLEFT JOIN strategy_group ON group.id = strategy_group.group_id;<\/pre>\n<p>\u8fd9\u4e2a\u67e5\u8be2\u8bed\u53e5\u5c06\u8fd4\u56de\u6240\u6709 strategy \u8868\u4e2d\u7684\u6570\u636e\uff0c\u5e76\u4e3a\u6ca1\u6709 group \u5bf9\u5e94\u7684 strategy \u884c\u8bbe\u7f6e gatewaymac \u503c\u4e3a defaultvalue\u3002<\/p>\n<p>\u4eca\u5929\u5173\u4e8e\u300a\u6570\u636e\u5e93\u5173\u8054\u67e5\u8be2\u4e2d\u5982\u4f55\u5c06\u7a7a\u503c\u8bbe\u7f6e\u4e3a\u9ed8\u8ba4\u503c\uff1f\u300b\u7684\u5185\u5bb9\u4ecb\u7ecd\u5c31\u5230\u6b64\u7ed3\u675f\uff0c\u5982\u679c\u6709\u4ec0\u4e48\u7591\u95ee\u6216\u8005\u5efa\u8bae\uff0c\u53ef\u4ee5\u5728\u4e3b\u673a\u5b9d\u8d1d\u516c\u4f17\u53f7\u4e0b\u591a\u591a\u56de\u590d\u4ea4\u6d41\uff1b\u6587\u4e2d\u82e5\u6709\u4e0d\u6b63\u4e4b\u5904\uff0c\u4e5f\u5e0c\u671b\u56de\u590d\u7559\u8a00\u4ee5\u544a\u77e5\uff01<\/p>\n<dl>\n<dt>\n <\/dt>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"<p>\u6570\u636e\u5e93\u5173\u8054\u67e5\u8be2\u4e2d\u5982\u4f55\u5c06\u7a7a\u503c\u8bbe\u7f6e\u4e3a&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-200379","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/200379","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=200379"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/200379\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=200379"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=200379"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=200379"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}