{"id":168975,"date":"2024-11-06T17:49:16","date_gmt":"2024-11-06T09:49:16","guid":{"rendered":"https:\/\/server.hk\/cnblog\/168975\/"},"modified":"2024-11-06T17:49:17","modified_gmt":"2024-11-06T09:49:17","slug":"%e9%9d%a2%e8%a9%a6%e5%ae%98%ef%bc%9amysql%e4%b8%adcount%e5%92%8ccount1%e5%93%aa%e5%80%8b%e6%95%88%e7%8e%87%e9%ab%98%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/168975\/","title":{"rendered":"\u9762\u8a66\u5b98\uff1aMySQL\u4e2dCount(*)\u548cCount(1)\u54ea\u500b\u6548\u7387\u9ad8\uff1f"},"content":{"rendered":"

\u9762\u8a66\u5b98\uff1aMySQL\u4e2dCount(*)\u548cCount(1)\u54ea\u500b\u6548\u7387\u9ad8\uff1f<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u5ee3\u6cdb\u4f7f\u7528\u7684\u95dc\u806f\u6578\u64da\u5eab\u7cfb\u7d71\u3002\u7576\u6211\u5011\u9700\u8981\u8a08\u7b97\u8868\u4e2d\u884c\u6578\u6642\uff0c\u7d93\u5e38\u6703\u4f7f\u7528\u5230 COUNT(*)<\/code> \u548c COUNT(1)<\/code> \u9019\u5169\u500b\u51fd\u6578\u3002\u96d6\u7136\u5b83\u5011\u7684\u529f\u80fd\u770b\u4f3c\u76f8\u4f3c\uff0c\u4f46\u5728\u6027\u80fd\u548c\u4f7f\u7528\u60c5\u5883\u4e0a\u537b\u5b58\u5728\u4e00\u4e9b\u5dee\u7570\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e\u9019\u5169\u8005\u7684\u6548\u7387\u554f\u984c\uff0c\u4e26\u63d0\u4f9b\u4e00\u4e9b\u5be6\u969b\u7684\u4f8b\u5b50\u4f86\u5e6b\u52a9\u7406\u89e3\u3002<\/p>\n

COUNT(*) \u8207 COUNT(1) \u7684\u57fa\u672c\u6982\u5ff5<\/h2>\n

COUNT(*)<\/code> \u662f\u7528\u4f86\u8a08\u7b97\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u5305\u62ec NULL \u503c\u3002\u9019\u610f\u5473\u8457\u7121\u8ad6\u884c\u4e2d\u7684\u6578\u64da\u662f\u5426\u5b58\u5728\uff0c\u9019\u500b\u51fd\u6578\u90fd\u6703\u5c07\u5176\u8a08\u5165\u5728\u5167\u3002\u76f8\u5c0d\u800c\u8a00\uff0cCOUNT(1)<\/code> \u4e5f\u662f\u7528\u4f86\u8a08\u7b97\u884c\u6578\uff0c\u4f46\u5b83\u662f\u8a08\u7b97\u6240\u6709\u884c\u4e2d\u503c\u70ba 1 \u7684\u884c\u6578\u3002\u7531\u65bc 1 \u662f\u4e00\u500b\u5e38\u6578\uff0c\u9019\u610f\u5473\u8457\u5b83\u6703\u5c0d\u6bcf\u4e00\u884c\u90fd\u8fd4\u56de 1\uff0c\u56e0\u6b64 COUNT(1)<\/code> \u4e5f\u6703\u8fd4\u56de\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\u3002<\/p>\n

\u6027\u80fd\u6bd4\u8f03<\/h2>\n

\u5728\u6027\u80fd\u65b9\u9762\uff0cCOUNT(*)<\/code> \u548c COUNT(1)<\/code> \u7684\u6548\u7387\u901a\u5e38\u662f\u76f8\u4f3c\u7684\u3002\u9019\u662f\u56e0\u70ba\u5728 MySQL \u7684\u57f7\u884c\u8a08\u5283\u4e2d\uff0c\u9019\u5169\u500b\u51fd\u6578\u90fd\u6703\u88ab\u512a\u5316\u70ba\u76f8\u540c\u7684\u67e5\u8a62\u8a08\u5283\u3002\u7121\u8ad6\u4f7f\u7528\u54ea\u4e00\u7a2e\u65b9\u5f0f\uff0cMySQL \u90fd\u6703\u6383\u63cf\u6574\u500b\u8868\u4f86\u8a08\u7b97\u884c\u6578\u3002<\/p>\n

\u7136\u800c\uff0c\u6839\u64da\u4e0d\u540c\u7684\u60c5\u6cc1\uff0c\u53ef\u80fd\u6703\u6709\u4e00\u4e9b\u5fae\u5c0f\u7684\u6027\u80fd\u5dee\u7570\u3002\u4f8b\u5982\uff0c\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0cCOUNT(*)<\/code> \u53ef\u80fd\u6703\u66f4\u5feb\uff0c\u56e0\u70ba\u5b83\u4e0d\u9700\u8981\u5c0d\u6bcf\u4e00\u884c\u9032\u884c\u984d\u5916\u7684\u8a08\u7b97\u3002\u800c COUNT(1)<\/code> \u5247\u9700\u8981\u5c0d\u6bcf\u4e00\u884c\u8fd4\u56de\u4e00\u500b\u5e38\u6578\u503c\uff0c\u9019\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\u53ef\u80fd\u6703\u7a0d\u5fae\u5f71\u97ff\u6027\u80fd\u3002<\/p>\n

\u5be6\u969b\u4f8b\u5b50<\/h2>\n

\u4ee5\u4e0b\u662f\u4f7f\u7528 COUNT(*)<\/code> \u548c COUNT(1)<\/code> \u7684\u7c21\u55ae SQL \u67e5\u8a62\u793a\u4f8b\uff1a<\/p>\n

SELECT COUNT(*) FROM users;<\/code><\/pre>\n
SELECT COUNT(1) FROM users;<\/code><\/pre>\n
\u9019\u5169\u500b\u67e5\u8a62\u90fd\u5c07\u8fd4\u56de users<\/code> \u8868\u4e2d\u7684\u884c\u6578\u3002\u70ba\u4e86\u9032\u4e00\u6b65\u9a57\u8b49\u6027\u80fd\u5dee\u7570\uff0c\u53ef\u4ee5\u4f7f\u7528 MySQL \u7684 EXPLAIN<\/code> \u8a9e\u53e5\u4f86\u67e5\u770b\u57f7\u884c\u8a08\u5283\uff1a<\/p>\n
EXPLAIN SELECT COUNT(*) FROM users;<\/code><\/pre>\n
EXPLAIN SELECT COUNT(1) FROM users;<\/code><\/pre>\n
\u57f7\u884c\u8a08\u5283\u5c07\u986f\u793a\u9019\u5169\u500b\u67e5\u8a62\u7684\u6210\u672c\u548c\u884c\u6578\uff0c\u901a\u5e38\u6703\u767c\u73fe\u5b83\u5011\u7684\u6210\u672c\u662f\u76f8\u4f3c\u7684\u3002<\/p>\n
\u7d50\u8ad6<\/h2>\n
\u7e3d\u7684\u4f86\u8aaa\uff0cCOUNT(*)<\/code> \u548c COUNT(1)<\/code> \u5728 MySQL \u4e2d\u7684\u6027\u80fd\u5dee\u7570\u5fae\u4e4e\u5176\u5fae\uff0c\u901a\u5e38\u53ef\u4ee5\u6839\u64da\u500b\u4eba\u559c\u597d\u6216\u5718\u968a\u7684\u7de8\u78bc\u98a8\u683c\u4f86\u9078\u64c7\u4f7f\u7528\u54ea\u4e00\u7a2e\u3002\u5c0d\u65bc\u5927\u591a\u6578\u61c9\u7528\u5834\u666f\u4f86\u8aaa\uff0c\u9019\u5169\u8005\u7684\u6548\u7387\u90fd\u662f\u8db3\u5920\u7684\u3002<\/p>\n
\u5728\u9078\u64c7\u5408\u9069\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\u6642\uff0c\u9664\u4e86\u8003\u616e\u67e5\u8a62\u6548\u7387\u5916\uff0c\u9084\u61c9\u8003\u616e\u5176\u4ed6\u56e0\u7d20\uff0c\u5982\u6578\u64da\u5eab\u7684\u53ef\u64f4\u5c55\u6027\u548c\u7a69\u5b9a\u6027\u3002\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684 VPS<\/a> \u89e3\u6c7a\u65b9\u6848\uff0cServer.HK \u63d0\u4f9b\u591a\u7a2e\u9078\u64c7\uff0c\u9069\u5408\u5404\u7a2e\u9700\u6c42\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u9762\u8a66\u5b98\u63a2\u8a0eMySQL\u4e2dCount(*)\u8207Count(1)\u7684\u6548\u7387\u5dee\u7570\uff0c\u63ed\u793a\u5169\u8005\u5728\u6027\u80fd\u4e0a\u7684\u5be6\u969b\u8868\u73fe\u8207\u4f7f\u7528\u60c5\u5883\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-168975","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168975","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=168975"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168975\/revisions"}],"predecessor-version":[{"id":168976,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/168975\/revisions\/168976"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=168975"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=168975"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=168975"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}