{"id":7171,"date":"2024-11-14T14:32:19","date_gmt":"2024-11-14T06:32:19","guid":{"rendered":"https:\/\/fwq.ai\/blog\/7171\/"},"modified":"2024-11-14T14:32:19","modified_gmt":"2024-11-14T06:32:19","slug":"mysql-%e6%9f%a5%e8%af%a2%e4%b8%ad%e5%a6%82%e4%bd%95%e5%8c%85%e5%90%ab%e8%a1%a8%e8%bf%9e%e6%8e%a5%e4%b8%ad%e5%80%bc%e4%b8%ba-0-%e7%9a%84%e8%ae%b0%e5%bd%95%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/7171\/","title":{"rendered":"MySQL \u67e5\u8be2\u4e2d\u5982\u4f55\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\uff1f"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/img.php.cn\/upload\/article\/001\/246\/273\/173055636433236.jpg\" class=\"aligncenter\" title=\"MySQL \u67e5\u8be2\u4e2d\u5982\u4f55\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\uff1f\u63d2\u56fe\" alt=\"MySQL \u67e5\u8be2\u4e2d\u5982\u4f55\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\uff1f\u63d2\u56fe\" \/><\/p>\n<p><strong>\u5982\u4f55\u4f7f  \u67e5\u8be2\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\uff1f<\/strong><\/p>\n<p>\u5728\u7ed9\u5b9a\u7684 mysql \u67e5\u8be2\u4e2d\uff0c\u5f53\u8fde\u63a5\u8868 d \u4e2d\u51fa\u73b0\u503c\u4e3a 0 \u65f6\uff0c\u5c06\u65e0\u6cd5\u67e5\u8be2\u5b8c\u6574\u8bb0\u5f55\u3002\u8fd9\u662f\u56e0\u4e3a\u67e5\u8be2\u4f7f\u7528\u4e86 inner join\uff0c\u5b83\u53ea\u80fd\u8fd4\u56de\u540c\u65f6\u6ee1\u8db3\u6240\u6709\u8fde\u63a5\u6761\u4ef6\u7684\u8bb0\u5f55\u3002<\/p>\n<p>\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u9700\u8981\u4f7f\u7528 left join\uff0c\u5b83\u53ef\u4ee5\u5728\u5176\u4e2d\u4e00\u4e2a\u8868\u7684\u8fde\u63a5\u6761\u4ef6\u4e0d\u6ee1\u8db3\u65f6\u4ecd\u7136\u8fd4\u56de\u8bb0\u5f55\u3002\u8fd9\u5c06\u786e\u4fdd\u67e5\u8be2\u53ef\u4ee5\u5305\u542b d \u8868\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\u3002<\/p>\n<p>\u56e0\u6b64\uff0c\u4fee\u6539\u540e\u7684\u67e5\u8be2\u5982\u4e0b\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>\u8fd9\u6837\u4fee\u6539\u540e\uff0c\u67e5\u8be2\u5c06\u8fd4\u56de\u6240\u6709 d \u8868\u8bb0\u5f55\uff0c\u5373\u4f7f\u5b83\u4eec\u5728\u5176\u4ed6\u8868\u4e2d\u6ca1\u6709\u5173\u8054\u3002\u5bf9\u4e8e\u6ca1\u6709\u5173\u8054\u7684 name \u503c\uff0c\u67e5\u8be2\u5c06\u663e\u793a\u4e3a null\u3002<\/p>\n<p>\u4ee5\u4e0a\u5c31\u662fMySQL \u67e5\u8be2\u4e2d\u5982\u4f55\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\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>\u5982\u4f55\u4f7f \u67e5\u8be2\u5305\u542b\u8868\u8fde\u63a5\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\uff1f \u5728\u7ed9\u5b9a\u7684 mysql \u67e5\u8be2\u4e2d\uff0c\u5f53\u8fde\u63a5\u8868 d \u4e2d\u51fa\u73b0\u503c\u4e3a 0 \u65f6\uff0c\u5c06\u65e0\u6cd5\u67e5\u8be2\u5b8c\u6574\u8bb0\u5f55\u3002\u8fd9\u662f\u56e0\u4e3a\u67e5\u8be2\u4f7f\u7528\u4e86 inner join\uff0c\u5b83\u53ea\u80fd\u8fd4\u56de\u540c\u65f6\u6ee1\u8db3\u6240\u6709\u8fde\u63a5\u6761\u4ef6\u7684\u8bb0\u5f55\u3002 \u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u9700\u8981\u4f7f\u7528 left join\uff0c\u5b83\u53ef\u4ee5\u5728\u5176\u4e2d\u4e00\u4e2a\u8868\u7684\u8fde\u63a5\u6761\u4ef6\u4e0d\u6ee1\u8db3\u65f6\u4ecd\u7136\u8fd4\u56de\u8bb0\u5f55\u3002\u8fd9\u5c06\u786e\u4fdd\u67e5\u8be2\u53ef\u4ee5\u5305\u542b d \u8868\u4e2d\u503c\u4e3a 0 \u7684\u8bb0\u5f55\u3002 \u56e0\u6b64\uff0c\u4fee\u6539\u540e\u7684\u67e5\u8be2\u5982\u4e0b\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 [&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-7171","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7171","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=7171"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7171\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=7171"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=7171"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=7171"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}