{"id":76694,"date":"2024-10-16T09:02:14","date_gmt":"2024-10-16T01:02:14","guid":{"rendered":"https:\/\/server.hk\/cnblog\/76694\/"},"modified":"2024-10-16T09:02:14","modified_gmt":"2024-10-16T01:02:14","slug":"mysql%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%adcount%e5%92%8cdistinct%e7%9a%84%e4%bd%bf%e7%94%a8%e5%8f%8a%e6%95%88%e7%8e%87%e7%a0%94%e7%a9%b6","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/76694\/","title":{"rendered":"MySQL\u6578\u64da\u5eab\u4e2dCOUNT(*)\u548cDISTINCT\u7684\u4f7f\u7528\u53ca\u6548\u7387\u7814\u7a76"},"content":{"rendered":"

MySQL\u6578\u64da\u5eab\u4e2dCOUNT(*)\u548cDISTINCT\u7684\u4f7f\u7528\u53ca\u6548\u7387\u7814\u7a76<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u5ee3\u6cdb\u4f7f\u7528\u7684\u95dc\u4fc2\u578b\u6578\u64da\u5eab\u7cfb\u7d71\u3002\u7576\u6211\u5011\u9700\u8981\u7d71\u8a08\u6578\u64da\u6642\uff0cCOUNT(*)\u548cDISTINCT\u662f\u5169\u500b\u5e38\u7528\u7684SQL\u51fd\u6578\u3002\u96d6\u7136\u5b83\u5011\u7684\u529f\u80fd\u76f8\u4f3c\uff0c\u4f46\u5728\u4f7f\u7528\u4e0a\u537b\u6709\u8457\u660e\u986f\u7684\u5dee\u7570\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e\u9019\u5169\u8005\u7684\u4f7f\u7528\u60c5\u5883\u53ca\u5176\u6548\u7387\uff0c\u5e6b\u52a9\u958b\u767c\u8005\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u505a\u51fa\u66f4\u660e\u667a\u7684\u9078\u64c7\u3002<\/p>\n

COUNT(*)\u7684\u4f7f\u7528<\/h2>\n

COUNT(*)\u51fd\u6578\u7528\u65bc\u8a08\u7b97\u67e5\u8a62\u7d50\u679c\u4e2d\u884c\u7684\u7e3d\u6578\u3002\u7121\u8ad6\u884c\u4e2d\u7684\u6578\u64da\u662f\u5426\u70baNULL\uff0cCOUNT(*)\u90fd\u6703\u5c07\u5176\u8a08\u7b97\u5728\u5167\u3002\u9019\u4f7f\u5f97COUNT(*)\u5728\u9700\u8981\u7372\u53d6\u8868\u4e2d\u6240\u6709\u884c\u6578\u6642\u975e\u5e38\u6709\u7528\u3002<\/p>\n

SELECT COUNT(*) FROM users;<\/code><\/pre>\n
\u4e0a\u8ff0\u67e5\u8a62\u5c07\u8fd4\u56deusers\u8868\u4e2d\u7684\u6240\u6709\u884c\u6578\u3002COUNT(*)\u7684\u512a\u52e2\u5728\u65bc\u5176\u7c21\u55ae\u6027\u548c\u9ad8\u6548\u6027\uff0c\u7279\u5225\u662f\u5728\u4e0d\u9700\u8981\u8003\u616e\u7279\u5b9a\u5217\u7684\u60c5\u6cc1\u4e0b\u3002<\/p>\n
DISTINCT\u7684\u4f7f\u7528<\/h2>\n
DISTINCT\u95dc\u9375\u5b57\u7528\u65bc\u9078\u64c7\u552f\u4e00\u7684\u503c\uff0c\u901a\u5e38\u8207COUNT\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u8a08\u7b97\u67d0\u4e00\u5217\u4e2d\u4e0d\u540c\u503c\u7684\u6578\u91cf\u3002\u9019\u5728\u9700\u8981\u6392\u9664\u91cd\u8907\u6578\u64da\u6642\u975e\u5e38\u6709\u7528\u3002<\/p>\n
SELECT COUNT(DISTINCT country) FROM users;<\/code><\/pre>\n
\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56deusers\u8868\u4e2d\u4e0d\u540c\u570b\u5bb6\u7684\u6578\u91cf\u3002\u4f7f\u7528DISTINCT\u53ef\u4ee5\u5e6b\u52a9\u6211\u5011\u7372\u5f97\u66f4\u5177\u4ee3\u8868\u6027\u7684\u6578\u64da\uff0c\u4f46\u5176\u6548\u7387\u901a\u5e38\u4f4e\u65bcCOUNT(*)\uff0c\u56e0\u70ba\u5b83\u9700\u8981\u9032\u884c\u984d\u5916\u7684\u8a08\u7b97\u4f86\u904e\u6ffe\u91cd\u8907\u503c\u3002<\/p>\n
\u6548\u7387\u6bd4\u8f03<\/h2>\n
\u5728\u6027\u80fd\u65b9\u9762\uff0cCOUNT(*)\u901a\u5e38\u6bd4COUNT(DISTINCT column_name)\u66f4\u5feb\u3002\u9019\u662f\u56e0\u70baCOUNT(*)\u53ea\u9700\u8a08\u7b97\u884c\u6578\uff0c\u800cCOUNT(DISTINCT column_name)\u9700\u8981\u5c0d\u6578\u64da\u9032\u884c\u6392\u5e8f\u548c\u53bb\u91cd\uff0c\u9019\u6703\u589e\u52a0\u8a08\u7b97\u7684\u8907\u96dc\u6027\u3002<\/p>\n
\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u5305\u542b100\u842c\u689d\u8a18\u9304\u7684users\u8868\uff0c\u4e26\u4e14country\u5217\u4e2d\u6709100\u500b\u4e0d\u540c\u7684\u570b\u5bb6\u3002\u4f7f\u7528COUNT(*)\u5c07\u76f4\u63a5\u8fd4\u56de1000000\uff0c\u800c\u4f7f\u7528COUNT(DISTINCT country)\u5247\u9700\u8981\u904d\u6b77\u6240\u6709\u8a18\u9304\uff0c\u4e26\u9032\u884c\u53bb\u91cd\uff0c\u9019\u6a23\u7684\u64cd\u4f5c\u6703\u6d88\u8017\u66f4\u591a\u7684\u6642\u9593\u548c\u8cc7\u6e90\u3002<\/p>\n
\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u8003\u91cf<\/h2>\n
\u5728\u9078\u64c7\u4f7f\u7528COUNT(*)\u9084\u662fCOUNT(DISTINCT)\u6642\uff0c\u958b\u767c\u8005\u61c9\u6839\u64da\u5177\u9ad4\u9700\u6c42\u4f86\u6c7a\u5b9a\u3002\u5982\u679c\u53ea\u9700\u8981\u7372\u53d6\u884c\u6578\uff0cCOUNT(*)\u662f\u6700\u4f73\u9078\u64c7\uff1b\u5982\u679c\u9700\u8981\u7372\u53d6\u552f\u4e00\u503c\u7684\u6578\u91cf\uff0c\u5247\u61c9\u4f7f\u7528COUNT(DISTINCT)\u3002<\/p>\n
\u6b64\u5916\uff0c\u5c0d\u65bc\u5927\u578b\u6578\u64da\u96c6\uff0c\u8003\u616e\u5230\u6027\u80fd\u554f\u984c\uff0c\u958b\u767c\u8005\u53ef\u4ee5\u8003\u616e\u4f7f\u7528\u7d22\u5f15\u4f86\u52a0\u901f\u67e5\u8a62\u3002\u5c0d\u65bc\u9700\u8981\u983b\u7e41\u67e5\u8a62\u7684\u5217\uff0c\u5efa\u7acb\u7d22\u5f15\u53ef\u4ee5\u986f\u8457\u63d0\u9ad8\u67e5\u8a62\u6548\u7387\u3002<\/p>\n
\u7d50\u8ad6<\/h2>\n
\u5728MySQL\u4e2d\uff0cCOUNT(*)\u548cDISTINCT\u5404\u6709\u5176\u7279\u5b9a\u7684\u4f7f\u7528\u5834\u666f\u548c\u6548\u7387\u8003\u91cf\u3002\u4e86\u89e3\u9019\u5169\u8005\u7684\u5dee\u7570\u53ca\u5176\u6027\u80fd\u5f71\u97ff\uff0c\u80fd\u5e6b\u52a9\u958b\u767c\u8005\u5728\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u505a\u51fa\u66f4\u6709\u6548\u7684\u6c7a\u7b56\u3002\u7121\u8ad6\u662f\u9032\u884c\u6578\u64da\u7d71\u8a08\u9084\u662f\u6578\u64da\u5206\u6790\uff0c\u9078\u64c7\u5408\u9069\u7684\u51fd\u6578\u5c07\u76f4\u63a5\u5f71\u97ff\u5230\u67e5\u8a62\u7684\u6548\u7387\u548c\u7d50\u679c\u7684\u6e96\u78ba\u6027\u3002<\/p>\n
\u5982\u9700\u9032\u4e00\u6b65\u4e86\u89e3\u5982\u4f55\u512a\u5316\u60a8\u7684\u6578\u64da\u5eab\u6027\u80fd\uff0c\u60a8\u53ef\u4ee5\u8003\u616e\u4f7f\u7528\u9999\u6e2fVPS<\/a>\u4f86\u63d0\u5347\u60a8\u7684\u61c9\u7528\u7a0b\u5e8f\u7684\u904b\u884c\u6548\u7387\u3002\u7121\u8ad6\u662f\u6578\u64da\u5eab\u7ba1\u7406\u9084\u662f\u5176\u4ed6\u670d\u52d9\uff0c\u9078\u64c7\u5408\u9069\u7684\u4f3a\u670d\u5668<\/a>\u5c07\u662f\u6210\u529f\u7684\u95dc\u9375\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u8a0eMySQL\u6578\u64da\u5eab\u4e2dCOUNT(*)\u8207DISTINCT\u7684\u4f7f\u7528\u65b9\u6cd5\u53ca\u5176\u6548\u7387\uff0c\u5e6b\u52a9\u512a\u5316\u67e5\u8a62\u6027\u80fd\u8207\u6578\u64da\u5206\u6790\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-76694","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76694","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=76694"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76694\/revisions"}],"predecessor-version":[{"id":76695,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76694\/revisions\/76695"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=76694"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=76694"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=76694"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}