{"id":7176,"date":"2024-11-14T11:29:50","date_gmt":"2024-11-14T03:29:50","guid":{"rendered":"https:\/\/fwq.ai\/blog\/7176\/"},"modified":"2024-11-14T11:29:50","modified_gmt":"2024-11-14T03:29:50","slug":"%e5%a6%82%e4%bd%95%e4%bd%bf%e7%94%a8%e5%a4%96%e8%bf%9e%e6%8e%a5%e5%9c%a8-mysql-%e4%b8%ad%e6%9f%a5%e8%af%a2%e5%85%b3%e8%81%94%e8%a1%a8%e5%b9%b6%e6%98%be%e7%a4%ba%e6%89%80%e6%9c%89%e8%ae%b0%e5%bd%95","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/7176\/","title":{"rendered":"\u5982\u4f55\u4f7f\u7528\u5916\u8fde\u63a5\u5728 MySQL \u4e2d\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\uff1f"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/001\/246\/273\/173059365170379.jpg\" class=\"aligncenter\" title=\"\u5982\u4f55\u4f7f\u7528\u5916\u8fde\u63a5\u5728 MySQL \u4e2d\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\uff1f\u63d2\u56fe\" alt=\"\u5982\u4f55\u4f7f\u7528\u5916\u8fde\u63a5\u5728 MySQL \u4e2d\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\uff1f\u63d2\u56fe\" \/><\/p>\n<p><strong> \u67e5\u8be2\u5173\u8054\u8868\u65f6\u663e\u793a\u6240\u6709\u8bb0\u5f55<\/strong><\/p>\n<p>\u5728\u6d89\u53ca\u591a\u4e2a\u8868\u7684\u67e5\u8be2\u4e2d\uff0c\u5982\u679c\u67d0\u4e2a\u8868\u4e2d\u6709\u503c\u4e3a 0 \u7684\u5b57\u6bb5\uff0c\u53ef\u80fd\u4f1a\u5bfc\u81f4\u67e5\u8be2\u4e0d\u5230\u4e0e\u5176\u5173\u8054\u7684\u6240\u6709\u8bb0\u5f55\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u53ef\u4ee5\u5728\u67e5\u8be2\u4e2d\u4f7f\u7528\u5916\u8fde\u63a5\uff08left join\uff09\u3002<\/p>\n<p>\u4ee5\u4e0b\u67e5\u8be2\u793a\u8303\u4e86\u5982\u4f55\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\uff0c\u5373\u4f7f\u5176\u4e2d\u67d0\u4e2a\u8868\u4e2d\u5305\u542b 0 \u7684\u503c\uff1a<\/p>\n<pre>SELECT d.id, a.name AS a_name, b.name AS b_name, c.name AS c_name\nFROM D AS d\nLEFT JOIN A AS a ON a.id=d.a_id\nLEFT JOIN B AS b ON b.id=d.b_id\nLEFT JOIN C AS c ON c.id=d.c_id;<\/pre>\n<p> \u767b\u5f55\u540e\u590d\u5236 <\/p>\n<p>\u5728\u8fd9\u4e2a\u67e5\u8be2\u4e2d\uff1a<\/p>\n<ul>\n<li>left join \u6307\u5b9a\u4e86\u5f53 a\u3001b \u6216 c \u8868\u4e2d\u6ca1\u6709\u5339\u914d\u8bb0\u5f55\u65f6\uff0c\u5c06\u8fd4\u56de null \u800c\u4e0d\u662f\u5ffd\u7565\u8be5\u884c\u3002<\/li>\n<li>a_name\u3001b_name \u548c c_name \u662f\u91cd\u547d\u540d\u7684\u5217\u540d\uff0c\u8868\u793a a\u3001b \u548c c \u8868\u4e2d\u7684 name \u5217\u3002<\/li>\n<\/ul>\n<p>\u8fd9\u6837\uff0c\u5373\u4f7f d \u8868\u4e2d\u67d0\u4e2a\u8bb0\u5f55\u7684 a_id\u3001b_id \u6216 c_id \u4e3a 0\uff0c\u6b64\u67e5\u8be2\u4ecd\u4f1a\u8fd4\u56de\u6240\u6709\u8bb0\u5f55\uff0c\u5e76\u5c06\u672a\u5173\u8054\u7684 name \u5217\u663e\u793a\u4e3a null\u3002<\/p>\n<p>\u4ee5\u4e0a\u5c31\u662f\u5982\u4f55\u4f7f\u7528\u5916\u8fde\u63a5\u5728 MySQL \u4e2d\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\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>\u67e5\u8be2\u5173\u8054\u8868\u65f6\u663e\u793a\u6240\u6709\u8bb0\u5f55 \u5728\u6d89\u53ca\u591a\u4e2a\u8868\u7684\u67e5\u8be2\u4e2d\uff0c\u5982\u679c\u67d0\u4e2a\u8868\u4e2d\u6709\u503c\u4e3a 0 \u7684\u5b57\u6bb5\uff0c\u53ef\u80fd\u4f1a\u5bfc\u81f4\u67e5\u8be2\u4e0d\u5230\u4e0e\u5176\u5173\u8054\u7684\u6240\u6709\u8bb0\u5f55\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u53ef\u4ee5\u5728\u67e5\u8be2\u4e2d\u4f7f\u7528\u5916\u8fde\u63a5\uff08left join\uff09\u3002 \u4ee5\u4e0b\u67e5\u8be2\u793a\u8303\u4e86\u5982\u4f55\u67e5\u8be2\u5173\u8054\u8868\u5e76\u663e\u793a\u6240\u6709\u8bb0\u5f55\uff0c\u5373\u4f7f\u5176\u4e2d\u67d0\u4e2a\u8868\u4e2d\u5305\u542b 0 \u7684\u503c\uff1a SELECT d.id, a.name AS a_name, b.name AS b_name, c.name AS c_name FROM D AS d LEFT JOIN A AS a ON a.id=d.a_id LEFT JOIN B AS b ON b.id=d.b_id LEFT JOIN C AS c ON c.id=d.c_id; \u767b\u5f55\u540e\u590d\u5236 \u5728\u8fd9\u4e2a\u67e5\u8be2\u4e2d\uff1a left join \u6307\u5b9a\u4e86\u5f53 a\u3001b \u6216 c \u8868\u4e2d\u6ca1\u6709\u5339\u914d\u8bb0\u5f55\u65f6\uff0c\u5c06\u8fd4\u56de null \u800c\u4e0d\u662f\u5ffd\u7565\u8be5\u884c\u3002 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-7176","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7176","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=7176"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7176\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=7176"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=7176"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=7176"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}