{"id":200945,"date":"2025-05-06T09:28:27","date_gmt":"2025-05-06T01:28:27","guid":{"rendered":"https:\/\/server.hk\/cnblog\/200945\/"},"modified":"2025-05-06T09:28:27","modified_gmt":"2025-05-06T01:28:27","slug":"%e5%a6%82%e4%bd%95%e4%bd%bf%e7%94%a8-sql-%e6%9f%a5%e8%af%a2%e5%8e%bb%e9%99%a4-left-join-%e4%b8%ad%e4%ba%a7%e7%94%9f%e7%9a%84%e9%87%8d%e5%a4%8d%e8%ae%b0%e5%bd%95%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/200945\/","title":{"rendered":"\u5982\u4f55\u4f7f\u7528 SQL \u67e5\u8be2\u53bb\u9664 LEFT JOIN \u4e2d\u4ea7\u751f\u7684\u91cd\u590d\u8bb0\u5f55\uff1f"},"content":{"rendered":"<p><b><\/b> <\/p>\n<h1>\u5982\u4f55\u4f7f\u7528 SQL \u67e5\u8be2\u53bb\u9664 LEFT JOIN \u4e2d\u4ea7\u751f\u7684\u91cd\u590d\u8bb0\u5f55\uff1f<\/h1>\n<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20241122\/173226748467404ddcdd8a1.jpg\" class=\"aligncenter\"><\/p>\n<p><strong>sql \u67e5\u8be2\u53bb\u9664\u91cd\u590d\u8bb0\u5f55<\/strong><\/p>\n<p>\u60a8\u6b63\u5728\u5904\u7406\u4e24\u5f20\u8868\uff0ca \u8868\u548c b \u8868\uff0c\u8bd5\u56fe\u6839\u636e a \u8868\u7684\u6570\u636e\u67e5\u8be2\u4e0d\u91cd\u590d\u7684\u7ed3\u679c\u3002\u76ee\u524d\uff0c\u60a8\u7684\u67e5\u8be2\u4f7f\u7528\u4e86 left join\uff0c\u4f46\u5728\u8ddf\u8e2a\u53f7\u4e0d\u540c\u65f6\uff0c\u5b83\u4f1a\u5bfc\u81f4\u91cd\u590d\u7684\u8bb0\u5f55\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8be2\uff1a<\/p>\n<pre>select *\nfrom a\nleft join (\n  select sid, max(tracking_number)\n  from b\n  group by sid\n) b\non a.sid = b.sid<\/pre>\n<p>\u8fd9\u4e2a\u67e5\u8be2\u4f7f\u7528 max() \u51fd\u6570\u627e\u51fa\u6bcf\u4e2a sid \u5bf9\u5e94\u7684\u6700\u5927\u8ddf\u8e2a\u53f7\u3002\u5bf9\u4e8e\u67d0\u4e9b\u6570\u636e\u5e93\uff0c\u4f8b\u5982 sqlite \u548c\u8f83\u65b0\u7248\u672c\u7684 mysql\uff0c\u60a8\u53ef\u80fd\u4e0d\u9700\u8981\u4f7f\u7528\u8be5\u51fd\u6570\uff0c\u800c\u53ea\u9700\u8981\u5728\u5b50\u67e5\u8be2\u4e2d\u9009\u62e9\u8ddf\u8e2a\u53f7\u5373\u53ef\u3002<\/p>\n<p>\u5982\u679c\u60a8\u9700\u8981\u4f7f\u7528\u8be5\u51fd\u6570\uff0c\u5e76\u4e14\u60a8\u7684\u6570\u636e\u5e93\u4e0d\u652f\u6301\u5b83\uff0c\u5219\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8be2\uff1a<\/p>\n<pre>select\n    a.*,\n    b.tracking_number,\n    b.is_cancel \nfrom a\nleft join (\n    select max(id) id, sid\n    from b\n    group by sid\n) x on a.sid = x.sid\nleft join b on x.id = b.id<\/pre>\n<p>\u8fd9\u4e2a\u67e5\u8be2\u4f7f\u7528 max(id) \u627e\u51fa\u5177\u6709\u6700\u5927 id \u7684\u8bb0\u5f55\u7684 id\u3002\u7136\u540e\uff0c\u5b83\u4f7f\u7528\u8be5 id \u4ece b \u8868\u4e2d\u9009\u62e9\u5176\u4ed6\u4fe1\u606f\u3002<\/p>\n<p>\u7ec8\u4e8e\u4ecb\u7ecd\u5b8c\u5566\uff01\u5c0f\u4f19\u4f34\u4eec\uff0c\u8fd9\u7bc7\u5173\u4e8e\u300a\u5982\u4f55\u4f7f\u7528 SQL \u67e5\u8be2\u53bb\u9664 LEFT JOIN \u4e2d\u4ea7\u751f\u7684\u91cd\u590d\u8bb0\u5f55\uff1f\u300b\u7684\u4ecb\u7ecd\u5e94\u8be5\u8ba9\u4f60\u6536\u83b7\u591a\u591a\u4e86\u5427\uff01\u6b22\u8fce\u5927\u5bb6\u6536\u85cf\u6216\u5206\u4eab\u7ed9\u66f4\u591a\u9700\u8981\u5b66\u4e60\u7684\u670b\u53cb\u5427~\u4e3b\u673a\u5b9d\u8d1d\u516c\u4f17\u53f7\u4e5f\u4f1a\u53d1\u5e03\u6570\u636e\u5e93\u76f8\u5173\u77e5\u8bc6\uff0c\u5feb\u6765\u5173\u6ce8\u5427\uff01<\/p>\n<dl>\n<dt>\n <\/dt>\n<\/dl>\n","protected":false},"excerpt":{"rendered":"<p>\u5982\u4f55\u4f7f\u7528 SQL \u67e5\u8be2\u53bb\u9664 LE&#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-200945","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/200945","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=200945"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/200945\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=200945"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=200945"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=200945"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}