{"id":76202,"date":"2024-10-16T04:42:15","date_gmt":"2024-10-15T20:42:15","guid":{"rendered":"https:\/\/server.hk\/cnblog\/76202\/"},"modified":"2024-10-16T04:42:15","modified_gmt":"2024-10-15T20:42:15","slug":"mysql%e5%85%a5%e9%96%80%ef%bc%9a%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b8%e8%bf%94%e5%9b%9e%e7%ac%a6%e5%90%88%e6%8c%87%e5%ae%9a%e6%a2%9d%e4%bb%b6%e7%9a%84%e8%a1%8c%e6%95%b8%e3%80%82","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/76202\/","title":{"rendered":"MySQL\u5165\u9580\uff1a\u4f7f\u7528COUNT()\u51fd\u6578\u8fd4\u56de\u7b26\u5408\u6307\u5b9a\u689d\u4ef6\u7684\u884c\u6578\u3002"},"content":{"rendered":"

MySQL\u5165\u9580\uff1a\u4f7f\u7528COUNT()\u51fd\u6578\u8fd4\u56de\u7b26\u5408\u6307\u5b9a\u689d\u4ef6\u7684\u884c\u6578<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u975e\u5e38\u6d41\u884c\u7684\u9078\u64c7\uff0c\u56e0\u70ba\u5b83\u7684\u9748\u6d3b\u6027\u548c\u5f37\u5927\u7684\u529f\u80fd\u3002\u672c\u6587\u5c07\u4ecb\u7d39\u5982\u4f55\u4f7f\u7528MySQL\u4e2d\u7684COUNT()\u51fd\u6578\u4f86\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\uff0c\u9019\u5c0d\u65bc\u6578\u64da\u5206\u6790\u548c\u5831\u544a\u751f\u6210\u975e\u5e38\u91cd\u8981\u3002<\/p>\n

\u4ec0\u9ebc\u662fCOUNT()\u51fd\u6578\uff1f<\/h2>\n

COUNT()\u51fd\u6578\u662fMySQL\u4e2d\u4e00\u500b\u805a\u5408\u51fd\u6578\uff0c\u7528\u65bc\u8a08\u7b97\u67e5\u8a62\u7d50\u679c\u4e2d\u884c\u7684\u6578\u91cf\u3002\u9019\u500b\u51fd\u6578\u53ef\u4ee5\u7528\u4f86\u8a08\u7b97\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u6216\u662f\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\u3002COUNT()\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n

SELECT COUNT(column_name) FROM table_name WHERE condition;<\/code><\/pre>\n
\u5728\u9019\u88e1\uff0ccolumn_name<\/code>\u662f\u4f60\u60f3\u8981\u8a08\u7b97\u7684\u5217\u540d\uff0ctable_name<\/code>\u662f\u6578\u64da\u8868\u7684\u540d\u7a31\uff0c\u800ccondition<\/code>\u5247\u662f\u4f60\u5e0c\u671b\u6eff\u8db3\u7684\u689d\u4ef6\u3002<\/p>\n
\u4f7f\u7528COUNT()\u51fd\u6578\u7684\u57fa\u672c\u793a\u4f8b<\/h2>\n
\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70baemployees<\/code>\u7684\u6578\u64da\u8868\uff0c\u8a72\u8868\u5305\u542b\u4ee5\u4e0b\u5217\uff1aid<\/code>\u3001name<\/code>\u3001department<\/code>\u548csalary<\/code>\u3002\u5982\u679c\u6211\u5011\u60f3\u8981\u8a08\u7b97\u6240\u6709\u54e1\u5de5\u7684\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n
SELECT COUNT(*) FROM employees;<\/code><\/pre>\n
\u9019\u5c07\u8fd4\u56deemployees<\/code>\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\u3002<\/p>\n
\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578<\/h2>\n
COUNT()\u51fd\u6578\u7684\u5f37\u5927\u4e4b\u8655\u5728\u65bc\u5b83\u53ef\u4ee5\u8207WHERE<\/code>\u5b50\u53e5\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u8981\u8a08\u7b97\u5728\u201c\u92b7\u552e\u201d\u90e8\u9580\u5de5\u4f5c\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n
SELECT COUNT(*) FROM employees WHERE department = 'Sales';<\/code><\/pre>\n
\u9019\u5c07\u8fd4\u56de\u6240\u6709\u5728\u201c\u92b7\u552e\u201d\u90e8\u9580\u5de5\u4f5c\u7684\u54e1\u5de5\u7684\u6578\u91cf\u3002<\/p>\n
\u4f7f\u7528DISTINCT\u95dc\u9375\u5b57<\/h2>\n
\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u6211\u5011\u53ef\u80fd\u53ea\u60f3\u8a08\u7b97\u552f\u4e00\u7684\u503c\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u8981\u8a08\u7b97\u4e0d\u540c\u90e8\u9580\u7684\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528DISTINCT<\/code>\u95dc\u9375\u5b57\uff1a<\/p>\n
SELECT COUNT(DISTINCT department) FROM employees;<\/code><\/pre>\n
\u9019\u5c07\u8fd4\u56deemployees<\/code>\u8868\u4e2d\u4e0d\u540c\u90e8\u9580\u7684\u6578\u91cf\uff0c\u800c\u4e0d\u6703\u91cd\u8907\u8a08\u7b97\u76f8\u540c\u7684\u90e8\u9580\u3002<\/p>\n
\u7d50\u5408GROUP BY\u5b50\u53e5<\/h2>\n
COUNT()\u51fd\u6578\u9084\u53ef\u4ee5\u8207GROUP BY<\/code>\u5b50\u53e5\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u4fbf\u6309\u7279\u5b9a\u5217\u9032\u884c\u5206\u7d44\u8a08\u7b97\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u8981\u6309\u90e8\u9580\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n
SELECT department, COUNT(*) FROM employees GROUP BY department;<\/code><\/pre>\n
\u9019\u5c07\u8fd4\u56de\u6bcf\u500b\u90e8\u9580\u53ca\u5176\u5c0d\u61c9\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u5e6b\u52a9\u6211\u5011\u66f4\u597d\u5730\u4e86\u89e3\u516c\u53f8\u5167\u90e8\u7684\u7d50\u69cb\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
COUNT()\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u975e\u5e38\u6709\u7528\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\u3002\u7121\u8ad6\u662f\u8a08\u7b97\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u9084\u662f\u6839\u64da\u7279\u5b9a\u689d\u4ef6\u9032\u884c\u7be9\u9078\uff0cCOUNT()\u51fd\u6578\u90fd\u80fd\u63d0\u4f9b\u7cbe\u78ba\u7684\u7d50\u679c\u3002\u901a\u904e\u7d50\u5408WHERE<\/code>\u3001DISTINCT<\/code>\u548cGROUP BY<\/code>\u7b49\u5b50\u53e5\uff0c\u4f7f\u7528\u8005\u53ef\u4ee5\u9748\u6d3b\u5730\u9032\u884c\u6578\u64da\u5206\u6790\u3002<\/p>\n
\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6709\u9032\u4e00\u6b65\u7684\u9700\u6c42\uff0c\u8003\u616e\u4f7f\u7528\u9999\u6e2fVPS<\/a>\u4f86\u642d\u5efa\u60a8\u7684MySQL\u74b0\u5883\uff0c\u4eab\u53d7\u66f4\u9ad8\u6548\u7684\u6578\u64da\u8655\u7406\u80fd\u529b\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5b78\u7fd2\u5982\u4f55\u5728MySQL\u4e2d\u4f7f\u7528COUNT()\u51fd\u6578\uff0c\u8f15\u9b06\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\uff0c\u63d0\u5347\u6578\u64da\u67e5\u8a62\u6548\u7387\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-76202","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76202","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=76202"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76202\/revisions"}],"predecessor-version":[{"id":76203,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/76202\/revisions\/76203"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=76202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=76202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=76202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}