{"id":166469,"date":"2024-11-05T16:18:35","date_gmt":"2024-11-05T08:18:35","guid":{"rendered":"https:\/\/server.hk\/cnblog\/166469\/"},"modified":"2024-11-05T16:18:37","modified_gmt":"2024-11-05T08:18:37","slug":"%e5%bf%ab%e9%80%9f%e5%8e%bb%e9%87%8d%ef%bc%9a%e6%95%b8%e6%93%9a%e5%ba%abselect%e8%aa%9e%e5%8f%a5%e5%84%aa%e5%8c%96%e6%8a%80%e5%b7%a7-%e6%95%b8%e6%93%9a%e5%ba%abselect%e5%8e%bb%e6%8e%89%e9%87%8d","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/166469\/","title":{"rendered":"\u5feb\u901f\u53bb\u91cd\uff1a\u6578\u64da\u5eabselect\u8a9e\u53e5\u512a\u5316\u6280\u5de7 (\u6578\u64da\u5eabselect\u53bb\u6389\u91cd\u8907\u8a18\u9304)"},"content":{"rendered":"

\u5feb\u901f\u53bb\u91cd\uff1a\u6578\u64da\u5eabselect\u8a9e\u53e5\u512a\u5316\u6280\u5de7 (\u6578\u64da\u5eabselect\u53bb\u6389\u91cd\u8907\u8a18\u9304)<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u91cd\u8907\u8a18\u9304\u7684\u5b58\u5728\u4e0d\u50c5\u6703\u5f71\u97ff\u67e5\u8a62\u6548\u7387\uff0c\u9084\u53ef\u80fd\u5c0e\u81f4\u6578\u64da\u4e0d\u4e00\u81f4\u6027\u3002\u56e0\u6b64\uff0c\u5982\u4f55\u6709\u6548\u5730\u53bb\u9664\u91cd\u8907\u8a18\u9304\u6210\u70ba\u4e86\u6578\u64da\u5eab\u512a\u5316\u7684\u91cd\u8981\u8ab2\u984c\u3002\u672c\u6587\u5c07\u63a2\u8a0e\u4e00\u4e9b\u512a\u5316 SELECT<\/code> \u8a9e\u53e5\u7684\u6280\u5de7\uff0c\u4ee5\u4fbf\u5feb\u901f\u53bb\u91cd\u4e26\u63d0\u9ad8\u67e5\u8a62\u6027\u80fd\u3002<\/p>\n

\u7406\u89e3\u91cd\u8907\u8a18\u9304\u7684\u4f86\u6e90<\/h2>\n

\u91cd\u8907\u8a18\u9304\u901a\u5e38\u662f\u7531\u65bc\u6578\u64da\u8f38\u5165\u932f\u8aa4\u3001\u6578\u64da\u5408\u4f75\u6216\u591a\u6b21\u5c0e\u5165\u76f8\u540c\u6578\u64da\u6240\u9020\u6210\u7684\u3002\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\uff0c\u61c9\u8003\u616e\u4f7f\u7528\u552f\u4e00\u7d04\u675f\uff08Unique Constraint\uff09\u4f86\u9632\u6b62\u91cd\u8907\u6578\u64da\u7684\u63d2\u5165\u3002\u7136\u800c\uff0c\u82e5\u5df2\u7d93\u5b58\u5728\u91cd\u8907\u8a18\u9304\uff0c\u5247\u9700\u8981\u63a1\u53d6\u63aa\u65bd\u4f86\u6e05\u7406\u9019\u4e9b\u6578\u64da\u3002<\/p>\n

\u4f7f\u7528DISTINCT\u95dc\u9375\u5b57<\/h2>\n

\u6700\u5e38\u898b\u7684\u53bb\u91cd\u65b9\u6cd5\u662f\u4f7f\u7528 DISTINCT<\/code> \u95dc\u9375\u5b57\u3002\u9019\u500b\u95dc\u9375\u5b57\u53ef\u4ee5\u5728\u67e5\u8a62\u4e2d\u6392\u9664\u91cd\u8907\u7684\u884c\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u7c21\u55ae\u7684\u793a\u4f8b\uff1a<\/p>\n

SELECT DISTINCT column1, column2 FROM table_name;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de table_name<\/code> \u4e2d column1<\/code> \u548c column2<\/code> \u7684\u552f\u4e00\u7d44\u5408\u3002\u96d6\u7136 DISTINCT<\/code> \u662f\u4e00\u500b\u7c21\u55ae\u6709\u6548\u7684\u89e3\u6c7a\u65b9\u6848\uff0c\u4f46\u5728\u8655\u7406\u5927\u91cf\u6578\u64da\u6642\uff0c\u6027\u80fd\u53ef\u80fd\u6703\u53d7\u5230\u5f71\u97ff\u3002<\/p>\n
\u4f7f\u7528GROUP BY\u8a9e\u53e5<\/h2>\n
\u53e6\u4e00\u7a2e\u53bb\u91cd\u7684\u65b9\u6cd5\u662f\u4f7f\u7528 GROUP BY<\/code> \u8a9e\u53e5\u3002\u9019\u7a2e\u65b9\u6cd5\u4e0d\u50c5\u53ef\u4ee5\u53bb\u9664\u91cd\u8907\u8a18\u9304\uff0c\u9084\u53ef\u4ee5\u9032\u884c\u805a\u5408\u8a08\u7b97\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u793a\u4f8b\uff1a<\/p>\n
SELECT column1, COUNT(*) FROM table_name GROUP BY column1;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de column1<\/code> \u7684\u552f\u4e00\u503c\u53ca\u5176\u51fa\u73fe\u7684\u6b21\u6578\u3002\u4f7f\u7528 GROUP BY<\/code> \u53ef\u4ee5\u5728\u53bb\u91cd\u7684\u540c\u6642\u7372\u53d6\u66f4\u591a\u7684\u6578\u64da\u4fe1\u606f\u3002<\/p>\n
\u4f7f\u7528\u5b50\u67e5\u8a62<\/h2>\n
\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u4f7f\u7528\u5b50\u67e5\u8a62\u53ef\u4ee5\u66f4\u9748\u6d3b\u5730\u53bb\u9664\u91cd\u8907\u8a18\u9304\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u60f3\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 * FROM orders WHERE order_id IN (SELECT MAX(order_id) FROM orders GROUP BY user_id);<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u8fd4\u56de\u6bcf\u500b\u7528\u6236\u7684\u6700\u65b0\u8a02\u55ae\uff0c\u907f\u514d\u4e86\u91cd\u8907\u8a18\u9304\u7684\u51fa\u73fe\u3002<\/p>\n
\u4f7f\u7528\u7a97\u53e3\u51fd\u6578<\/h2>\n
\u5728\u67d0\u4e9b\u6578\u64da\u5eab\u7cfb\u7d71\u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528\u7a97\u53e3\u51fd\u6578\u4f86\u53bb\u9664\u91cd\u8907\u8a18\u9304\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u4f7f\u7528\u7a97\u53e3\u51fd\u6578\u7684\u793a\u4f8b\uff1a<\/p>\n
SELECT * FROM (SELECT column1, ROW_NUMBER() OVER (PARTITION BY column1 ORDER BY column2) AS row_num FROM table_name) AS temp WHERE row_num = 1;<\/code><\/pre>\n
\u9019\u689d\u8a9e\u53e5\u5c07\u70ba\u6bcf\u500b column1<\/code> \u7684\u503c\u5206\u914d\u4e00\u500b\u884c\u865f\uff0c\u7136\u5f8c\u53ea\u9078\u64c7\u884c\u865f\u70ba1\u7684\u8a18\u9304\uff0c\u5f9e\u800c\u53bb\u9664\u91cd\u8907\u9805\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
\u53bb\u9664\u6578\u64da\u5eab\u4e2d\u7684\u91cd\u8907\u8a18\u9304\u662f\u63d0\u9ad8\u67e5\u8a62\u6548\u7387\u548c\u6578\u64da\u8cea\u91cf\u7684\u91cd\u8981\u6b65\u9a5f\u3002\u901a\u904e\u4f7f\u7528 DISTINCT<\/code>\u3001GROUP BY<\/code>\u3001\u5b50\u67e5\u8a62\u548c\u7a97\u53e3\u51fd\u6578\u7b49\u6280\u8853\uff0c\u53ef\u4ee5\u6709\u6548\u5730\u6e05\u7406\u6578\u64da\u4e26\u512a\u5316\u67e5\u8a62\u6027\u80fd\u3002\u5c0d\u65bc\u9700\u8981\u9ad8\u6548\u6578\u64da\u8655\u7406\u7684\u61c9\u7528\uff0c\u9078\u64c7\u5408\u9069\u7684\u6578\u64da\u5eab\u548c\u914d\u7f6e\u5408\u9069\u7684 VPS<\/a> \u74b0\u5883\u4e5f\u662f\u81f3\u95dc\u91cd\u8981\u7684\u3002\u4e86\u89e3\u9019\u4e9b\u6280\u5de7\u5f8c\uff0c\u60a8\u53ef\u4ee5\u66f4\u597d\u5730\u7ba1\u7406\u548c\u512a\u5316\u60a8\u7684\u6578\u64da\u5eab\uff0c\u78ba\u4fdd\u6578\u64da\u7684\u6e96\u78ba\u6027\u548c\u4e00\u81f4\u6027\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u638c\u63e1\u6578\u64da\u5eabselect\u8a9e\u53e5\u512a\u5316\u6280\u5de7\uff0c\u5feb\u901f\u53bb\u91cd\u4e26\u6709\u6548\u53bb\u6389\u91cd\u8907\u8a18\u9304\uff0c\u63d0\u5347\u67e5\u8a62\u6548\u7387\uff0c\u512a\u5316\u6578\u64da\u7ba1\u7406\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-166469","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/166469","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=166469"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/166469\/revisions"}],"predecessor-version":[{"id":166470,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/166469\/revisions\/166470"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=166469"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=166469"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=166469"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}