{"id":175189,"date":"2024-11-08T03:47:32","date_gmt":"2024-11-07T19:47:32","guid":{"rendered":"https:\/\/server.hk\/cnblog\/175189\/"},"modified":"2024-11-08T03:47:33","modified_gmt":"2024-11-07T19:47:33","slug":"%e5%a6%82%e4%bd%95%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b8%e5%9c%a8%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%b5%b1%e8%a8%88%e6%95%b8%e6%93%9a%e9%87%8f%ef%bc%9f-count%e5%9c%a8%e6%95%b8%e6%93%9a","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/175189\/","title":{"rendered":"\u5982\u4f55\u4f7f\u7528count\u51fd\u6578\u5728\u6578\u64da\u5eab\u4e2d\u7d71\u8a08\u6578\u64da\u91cf\uff1f (count\u5728\u6578\u64da\u5eab)"},"content":{"rendered":"<h1 id=\"%e5%a6%82%e4%bd%95%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b8%e5%9c%a8%e6%95%b8%e6%93%9a%e5%ba%ab%e4%b8%ad%e7%b5%b1%e8%a8%88%e6%95%b8%e6%93%9a%e9%87%8f%ef%bc%9f-aRRlpXilmE\">\u5982\u4f55\u4f7f\u7528count\u51fd\u6578\u5728\u6578\u64da\u5eab\u4e2d\u7d71\u8a08\u6578\u64da\u91cf\uff1f<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0c\u7d71\u8a08\u6578\u64da\u91cf\u662f\u4e00\u9805\u57fa\u672c\u800c\u91cd\u8981\u7684\u4efb\u52d9\u3002\u7121\u8ad6\u662f\u5206\u6790\u7528\u6236\u884c\u70ba\u3001\u751f\u6210\u5831\u544a\uff0c\u9084\u662f\u9032\u884c\u6578\u64da\u6316\u6398\uff0c\u4e86\u89e3\u6578\u64da\u7684\u6578\u91cf\u90fd\u662f\u81f3\u95dc\u91cd\u8981\u7684\u3002SQL\u4e2d\u7684 <code>COUNT<\/code> \u51fd\u6578\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u7372\u53d6\u6578\u64da\u91cf\u7684\u7d71\u8a08\u4fe1\u606f\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e <code>COUNT<\/code> \u51fd\u6578\u7684\u7528\u6cd5\u53ca\u5176\u5728\u6578\u64da\u5eab\u4e2d\u7684\u61c9\u7528\u3002<\/p>\n<h2 id=\"%e4%bb%80%e9%ba%bc%e6%98%afcount%e5%87%bd%e6%95%b8%ef%bc%9f-aRRlpXilmE\">\u4ec0\u9ebc\u662fCOUNT\u51fd\u6578\uff1f<\/h2>\n<p><code>COUNT<\/code> \u51fd\u6578\u662fSQL\u4e2d\u7528\u4f86\u8a08\u7b97\u884c\u6578\u7684\u805a\u5408\u51fd\u6578\u3002\u5b83\u53ef\u4ee5\u7528\u4f86\u8a08\u7b97\u8868\u4e2d\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\uff0c\u6216\u8005\u8a08\u7b97\u6574\u500b\u8868\u7684\u884c\u6578\u3002\u9019\u4f7f\u5f97 <code>COUNT<\/code> \u51fd\u6578\u5728\u6578\u64da\u5206\u6790\u548c\u5831\u544a\u751f\u6210\u4e2d\u975e\u5e38\u6709\u7528\u3002<\/p>\n<h2 id=\"count%e5%87%bd%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e8%aa%9e%e6%b3%95-aRRlpXilmE\">COUNT\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<p>\u4f7f\u7528 <code>COUNT<\/code> \u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>SELECT COUNT(column_name) FROM table_name WHERE condition;<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c<code>column_name<\/code> \u662f\u4f60\u60f3\u8981\u8a08\u7b97\u7684\u5217\u540d\uff0c<code>table_name<\/code> \u662f\u6578\u64da\u8868\u7684\u540d\u7a31\uff0c\u800c <code>condition<\/code> \u662f\u53ef\u9078\u7684\u689d\u4ef6\uff0c\u7528\u65bc\u904e\u6ffe\u6578\u64da\u3002<\/p>\n<h2 id=\"count%e5%87%bd%e6%95%b8%e7%9a%84%e4%bd%bf%e7%94%a8%e7%a4%ba%e4%be%8b-aRRlpXilmE\">COUNT\u51fd\u6578\u7684\u4f7f\u7528\u793a\u4f8b<\/h2>\n<h3 id=\"1-%e8%a8%88%e7%ae%97%e6%95%b4%e5%80%8b%e8%a1%a8%e7%9a%84%e8%a1%8c%e6%95%b8-aRRlpXilmE\">1. \u8a08\u7b97\u6574\u500b\u8868\u7684\u884c\u6578<\/h3>\n<p>\u5982\u679c\u4f60\u60f3\u8981\u8a08\u7b97\u4e00\u500b\u540d\u70ba <code>users<\/code> \u7684\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0bSQL\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM users;<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de <code>users<\/code> \u8868\u4e2d\u7684\u7e3d\u884c\u6578\u3002<\/p>\n<h3 id=\"2-%e8%a8%88%e7%ae%97%e7%89%b9%e5%ae%9a%e5%88%97%e7%9a%84%e9%9d%9e%e7%a9%ba%e5%80%bc%e6%95%b8%e9%87%8f-aRRlpXilmE\">2. \u8a08\u7b97\u7279\u5b9a\u5217\u7684\u975e\u7a7a\u503c\u6578\u91cf<\/h3>\n<p>\u5982\u679c\u4f60\u53ea\u60f3\u8a08\u7b97\u67d0\u4e00\u5217\uff08\u4f8b\u5982 <code>email<\/code>\uff09\u4e2d\u975e\u7a7a\u503c\u7684\u6578\u91cf\uff0c\u53ef\u4ee5\u9019\u6a23\u5beb\uff1a<\/p>\n<pre><code>SELECT COUNT(email) FROM users;<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de <code>email<\/code> \u5217\u4e2d\u6240\u6709\u975e\u7a7a\u503c\u7684\u6578\u91cf\u3002<\/p>\n<h3 id=\"3-%e4%bd%bf%e7%94%a8where%e5%ad%90%e5%8f%a5%e9%80%b2%e8%a1%8c%e6%a2%9d%e4%bb%b6%e8%a8%88%e7%ae%97-aRRlpXilmE\">3. \u4f7f\u7528WHERE\u5b50\u53e5\u9032\u884c\u689d\u4ef6\u8a08\u7b97<\/h3>\n<p>\u4f60\u9084\u53ef\u4ee5\u4f7f\u7528 <code>WHERE<\/code> \u5b50\u53e5\u4f86\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u6578\u3002\u4f8b\u5982\uff0c\u8a08\u7b97\u6240\u6709\u5e74\u9f61\u5927\u65bc30\u6b72\u7684\u7528\u6236\u6578\u91cf\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM users WHERE age &gt; 30;<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de\u5e74\u9f61\u5927\u65bc30\u6b72\u7684\u7528\u6236\u6578\u91cf\u3002<\/p>\n<h2 id=\"count%e5%87%bd%e6%95%b8%e7%9a%84%e9%80%b2%e9%9a%8e%e7%94%a8%e6%b3%95-aRRlpXilmE\">COUNT\u51fd\u6578\u7684\u9032\u968e\u7528\u6cd5<\/h2>\n<p>\u9664\u4e86\u57fa\u672c\u7684\u7528\u6cd5\uff0c<code>COUNT<\/code> \u51fd\u6578\u9084\u53ef\u4ee5\u8207\u5176\u4ed6SQL\u51fd\u6578\u7d50\u5408\u4f7f\u7528\uff0c\u4ee5\u7372\u53d6\u66f4\u8907\u96dc\u7684\u7d71\u8a08\u4fe1\u606f\u3002\u4f8b\u5982\uff0c\u8207 <code>GROUP BY<\/code> \u5b50\u53e5\u7d50\u5408\u4f7f\u7528\uff0c\u53ef\u4ee5\u6309\u67d0\u4e00\u5217\u9032\u884c\u5206\u7d44\u7d71\u8a08\uff1a<\/p>\n<pre><code>SELECT age, COUNT(*) FROM users GROUP BY age;<\/code><\/pre>\n<p>\u9019\u5c07\u8fd4\u56de\u6bcf\u500b\u5e74\u9f61\u6bb5\u7684\u7528\u6236\u6578\u91cf\u3002<\/p>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-aRRlpXilmE\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li>\u4f7f\u7528 <code>COUNT(*)<\/code> \u53ef\u4ee5\u8a08\u7b97\u6240\u6709\u884c\uff0c\u5305\u62ec\u7a7a\u503c\u3002<\/li>\n<li>\u4f7f\u7528 <code>COUNT(column_name)<\/code> \u53ea\u8a08\u7b97\u8a72\u5217\u4e2d\u7684\u975e\u7a7a\u503c\u3002<\/li>\n<li>\u5728\u4f7f\u7528 <code>GROUP BY<\/code> \u6642\uff0c\u6240\u6709\u975e\u805a\u5408\u5217\u5fc5\u9808\u51fa\u73fe\u5728 <code>GROUP BY<\/code> \u5b50\u53e5\u4e2d\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-aRRlpXilmE\">\u7e3d\u7d50<\/h2>\n<p>\u5728\u6578\u64da\u5eab\u4e2d\uff0c<code>COUNT<\/code> \u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u6709\u7528\u7684\u5de5\u5177\uff0c\u53ef\u4ee5\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u7372\u53d6\u6578\u64da\u91cf\u7684\u7d71\u8a08\u4fe1\u606f\u3002\u7121\u8ad6\u662f\u8a08\u7b97\u6574\u500b\u8868\u7684\u884c\u6578\uff0c\u9084\u662f\u6839\u64da\u7279\u5b9a\u689d\u4ef6\u9032\u884c\u7d71\u8a08\uff0c<code>COUNT<\/code> \u51fd\u6578\u90fd\u80fd\u63d0\u4f9b\u6709\u6548\u7684\u89e3\u6c7a\u65b9\u6848\u3002\u638c\u63e1 <code>COUNT<\/code> \u51fd\u6578\u7684\u4f7f\u7528\uff0c\u5c07\u6709\u52a9\u65bc\u63d0\u5347\u6578\u64da\u5206\u6790\u7684\u6548\u7387\u548c\u6e96\u78ba\u6027\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u670d\u52d9\u6709\u8208\u8da3\uff0c\u6216\u60f3\u4e86\u89e3\u66f4\u591a\u95dc\u65bc <a href=\"https:\/\/server.hk\">\u4e91\u670d\u52a1\u5668<\/a> \u7684\u4fe1\u606f\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3\u5982\u4f55\u5728\u6578\u64da\u5eab\u4e2d\u4f7f\u7528COUNT\u51fd\u6578\u4f86\u7d71\u8a08\u6578\u64da\u91cf\uff0c\u7c21\u5316\u6578\u64da\u5206\u6790\uff0c\u63d0\u5347\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-175189","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/175189","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=175189"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/175189\/revisions"}],"predecessor-version":[{"id":175190,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/175189\/revisions\/175190"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=175189"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=175189"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=175189"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}