{"id":172515,"date":"2024-11-07T13:46:16","date_gmt":"2024-11-07T05:46:16","guid":{"rendered":"https:\/\/server.hk\/cnblog\/172515\/"},"modified":"2024-11-07T13:46:17","modified_gmt":"2024-11-07T05:46:17","slug":"%e5%a6%82%e4%bd%95%e9%81%bf%e5%85%8d%e6%95%b8%e6%93%9a%e5%ba%ab%e6%9f%a5%e8%a9%a2%e5%b1%ac%e6%80%a7%e9%87%8d%e8%a4%87%e9%a1%af%e7%a4%ba%ef%bc%9f-%e6%95%b8%e6%93%9a%e5%ba%ab%e6%9f%a5%e8%a9%a2%e5%b1%ac","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/172515\/","title":{"rendered":"\u5982\u4f55\u907f\u514d\u6578\u64da\u5eab\u67e5\u8a62\u5c6c\u6027\u91cd\u8907\u986f\u793a\uff1f (\u6578\u64da\u5eab\u67e5\u8a62\u5c6c\u6027\u4e0d\u91cd\u8907\u986f\u793a\u4e0d\u51fa\u4f86)"},"content":{"rendered":"

\u5982\u4f55\u907f\u514d\u6578\u64da\u5eab\u67e5\u8a62\u5c6c\u6027\u91cd\u8907\u986f\u793a\uff1f<\/h1>\n

\u5728\u958b\u767c\u61c9\u7528\u7a0b\u5e8f\u6642\uff0c\u6578\u64da\u5eab\u67e5\u8a62\u662f\u4e0d\u53ef\u6216\u7f3a\u7684\u4e00\u90e8\u5206\u3002\u7136\u800c\uff0c\u7576\u67e5\u8a62\u7d50\u679c\u4e2d\u51fa\u73fe\u5c6c\u6027\u91cd\u8907\u986f\u793a\u7684\u60c5\u6cc1\u6642\uff0c\u6703\u5f71\u97ff\u6578\u64da\u7684\u53ef\u8b80\u6027\u548c\u61c9\u7528\u7684\u6027\u80fd\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u5982\u4f55\u907f\u514d\u6578\u64da\u5eab\u67e5\u8a62\u5c6c\u6027\u91cd\u8907\u986f\u793a\u7684\u554f\u984c\uff0c\u4e26\u63d0\u4f9b\u4e00\u4e9b\u5be6\u7528\u7684\u89e3\u6c7a\u65b9\u6848\u548c\u793a\u4f8b\u3002<\/p>\n

\u7406\u89e3\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u7684\u91cd\u8907\u5c6c\u6027<\/h2>\n

\u5728\u6578\u64da\u5eab\u4e2d\uff0c\u91cd\u8907\u5c6c\u6027\u901a\u5e38\u662f\u7531\u65bc\u4e0d\u7576\u7684\u67e5\u8a62\u8a2d\u8a08\u6216\u6578\u64da\u7d50\u69cb\u5f15\u8d77\u7684\u3002\u7576\u591a\u500b\u8868\u4e4b\u9593\u5b58\u5728\u95dc\u806f\u6642\uff0c\u82e5\u5728\u67e5\u8a62\u4e2d\u672a\u6b63\u78ba\u4f7f\u7528\u806f\u63a5\uff08JOIN\uff09\u6216\u904e\u6ffe\u689d\u4ef6\uff0c\u5247\u53ef\u80fd\u5c0e\u81f4\u76f8\u540c\u7684\u5c6c\u6027\u5728\u7d50\u679c\u96c6\u4e2d\u91cd\u8907\u986f\u793a\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6709\u5169\u500b\u8868\uff1ausers<\/code>\u548corders<\/code>\uff0c\u82e5\u6211\u5011\u60f3\u67e5\u8a62\u6bcf\u500b\u7528\u6236\u53ca\u5176\u8a02\u55ae\uff0c\u53ef\u80fd\u6703\u51fa\u73fe\u7528\u6236\u4fe1\u606f\u91cd\u8907\u7684\u60c5\u6cc1\u3002<\/p>\n

\u907f\u514d\u91cd\u8907\u986f\u793a\u7684\u7b56\u7565<\/h2>\n

1. \u4f7f\u7528DISTINCT\u95dc\u9375\u5b57<\/h3>\n

\u5728SQL\u67e5\u8a62\u4e2d\uff0c\u4f7f\u7528DISTINCT<\/code>\u95dc\u9375\u5b57\u53ef\u4ee5\u5e6b\u52a9\u904e\u6ffe\u6389\u91cd\u8907\u7684\u884c\u3002\u9019\u5c0d\u65bc\u7c21\u55ae\u7684\u67e5\u8a62\u7279\u5225\u6709\u6548\u3002<\/p>\n

SELECT DISTINCT username FROM users;<\/code><\/pre>\n
\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u552f\u4e00\u7684\u7528\u6236\u540d\uff0c\u907f\u514d\u4e86\u91cd\u8907\u986f\u793a\u7684\u554f\u984c\u3002<\/p>\n
2. \u6b63\u78ba\u4f7f\u7528JOIN\u8a9e\u53e5<\/h3>\n
\u5728\u6d89\u53ca\u591a\u500b\u8868\u7684\u67e5\u8a62\u4e2d\uff0c\u6b63\u78ba\u4f7f\u7528JOIN<\/code>\u8a9e\u53e5\u662f\u95dc\u9375\u3002\u78ba\u4fdd\u53ea\u9078\u64c7\u9700\u8981\u7684\u5217\uff0c\u4e26\u4f7f\u7528\u9069\u7576\u7684\u689d\u4ef6\u4f86\u904e\u6ffe\u7d50\u679c\u3002<\/p>\n
SELECT u.username, o.order_id \nFROM users u \nJOIN orders o ON u.id = o.user_id;<\/code><\/pre>\n
\u9019\u6a23\u7684\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u7528\u6236\u53ca\u5176\u8a02\u55ae\u7684\u552f\u4e00\u7d44\u5408\uff0c\u907f\u514d\u4e86\u7528\u6236\u4fe1\u606f\u7684\u91cd\u8907\u986f\u793a\u3002<\/p>\n
3. \u4f7f\u7528GROUP BY\u8a9e\u53e5<\/h3>\n
\u7576\u9700\u8981\u5c0d\u67e5\u8a62\u7d50\u679c\u9032\u884c\u5206\u7d44\u6642\uff0c\u53ef\u4ee5\u4f7f\u7528GROUP BY<\/code>\u8a9e\u53e5\u3002\u9019\u4e0d\u50c5\u53ef\u4ee5\u907f\u514d\u91cd\u8907\u986f\u793a\uff0c\u9084\u80fd\u9032\u884c\u805a\u5408\u8a08\u7b97\u3002<\/p>\n
SELECT username, COUNT(order_id) as order_count \nFROM users u \nJOIN orders o ON u.id = o.user_id \nGROUP BY username;<\/code><\/pre>\n
\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u7528\u6236\u53ca\u5176\u8a02\u55ae\u6578\u91cf\uff0c\u4e26\u4e14\u4e0d\u6703\u91cd\u8907\u986f\u793a\u7528\u6236\u540d\u3002<\/p>\n
4. \u4f7f\u7528\u5b50\u67e5\u8a62<\/h3>\n
\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u4f7f\u7528\u5b50\u67e5\u8a62\u53ef\u4ee5\u6709\u6548\u5730\u907f\u514d\u91cd\u8907\u986f\u793a\u3002\u4f8b\u5982\uff0c\u82e5\u8981\u67e5\u8a62\u6bcf\u500b\u7528\u6236\u7684\u6700\u65b0\u8a02\u55ae\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n
SELECT u.username, \n       (SELECT MAX(order_date) \n        FROM orders o \n        WHERE o.user_id = u.id) as latest_order \nFROM users u;<\/code><\/pre>\n
\u9019\u6a23\u7684\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u7528\u6236\u53ca\u5176\u6700\u65b0\u8a02\u55ae\u7684\u65e5\u671f\uff0c\u907f\u514d\u4e86\u91cd\u8907\u986f\u793a\u7684\u554f\u984c\u3002<\/p>\n
\u7d50\u8ad6<\/h2>\n
\u907f\u514d\u6578\u64da\u5eab\u67e5\u8a62\u5c6c\u6027\u91cd\u8907\u986f\u793a\u7684\u95dc\u9375\u5728\u65bc\u6b63\u78ba\u8a2d\u8a08\u67e5\u8a62\u8a9e\u53e5\u3002\u901a\u904e\u4f7f\u7528DISTINCT<\/code>\u3001JOIN<\/code>\u3001GROUP BY<\/code>\u548c\u5b50\u67e5\u8a62\u7b49\u6280\u8853\uff0c\u53ef\u4ee5\u6709\u6548\u5730\u904e\u6ffe\u91cd\u8907\u6578\u64da\uff0c\u63d0\u5347\u67e5\u8a62\u7d50\u679c\u7684\u53ef\u8b80\u6027\u548c\u6027\u80fd\u3002\u5c0d\u65bc\u958b\u767c\u8005\u4f86\u8aaa\uff0c\u7406\u89e3\u9019\u4e9b\u57fa\u672c\u6982\u5ff5\u662f\u81f3\u95dc\u91cd\u8981\u7684\uff0c\u9019\u5c07\u6709\u52a9\u65bc\u69cb\u5efa\u66f4\u9ad8\u6548\u7684\u6578\u64da\u5eab\u61c9\u7528\u3002<\/p>\n
\u5982\u9700\u4e86\u89e3\u66f4\u591a\u6709\u95dcVPS<\/a><\/code>\u548c\u6578\u64da\u5eab\u7ba1\u7406\u7684\u8cc7\u8a0a\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5b78\u7fd2\u5982\u4f55\u907f\u514d\u6578\u64da\u5eab\u67e5\u8a62\u4e2d\u5c6c\u6027\u91cd\u8907\u986f\u793a\uff0c\u63d0\u5347\u67e5\u8a62\u6548\u7387\uff0c\u78ba\u4fdd\u7d50\u679c\u6e05\u6670\u4e14\u6613\u65bc\u7406\u89e3\u3002<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-172515","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/172515","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"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=172515"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/172515\/revisions"}],"predecessor-version":[{"id":172516,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/172515\/revisions\/172516"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=172515"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=172515"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=172515"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}