{"id":180896,"date":"2024-11-09T14:05:15","date_gmt":"2024-11-09T06:05:15","guid":{"rendered":"https:\/\/server.hk\/cnblog\/180896\/"},"modified":"2024-11-09T14:05:16","modified_gmt":"2024-11-09T06:05:16","slug":"%e6%b7%b1%e5%85%a5%e4%ba%86%e8%a7%a3%e6%95%b8%e6%93%9a%e5%ba%abcount%e6%93%8d%e4%bd%9c%e7%9a%84%e5%90%ab%e7%be%a9%e8%88%87%e4%bd%9c%e7%94%a8-%e6%95%b8%e6%93%9a%e5%ba%abcount%e7%9a%84%e6%84%8f","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/180896\/","title":{"rendered":"\u6df1\u5165\u4e86\u89e3\u6578\u64da\u5eabcount\u64cd\u4f5c\u7684\u542b\u7fa9\u8207\u4f5c\u7528 (\u6578\u64da\u5eabcount\u7684\u610f\u601d)"},"content":{"rendered":"<h1 id=\"%e6%b7%b1%e5%85%a5%e4%ba%86%e8%a7%a3%e6%95%b8%e6%93%9a%e5%ba%abcount%e6%93%8d%e4%bd%9c%e7%9a%84%e5%90%ab%e7%be%a9%e8%88%87%e4%bd%9c%e7%94%a8-rWImMKsaUR\">\u6df1\u5165\u4e86\u89e3\u6578\u64da\u5eabcount\u64cd\u4f5c\u7684\u542b\u7fa9\u8207\u4f5c\u7528<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0c<strong>COUNT<\/strong> \u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u91cd\u8981\u7684\u805a\u5408\u51fd\u6578\uff0c\u5b83\u7528\u65bc\u8a08\u7b97\u67e5\u8a62\u7d50\u679c\u4e2d\u884c\u7684\u6578\u91cf\u3002\u7121\u8ad6\u662f\u5728\u6578\u64da\u5206\u6790\u3001\u5831\u544a\u751f\u6210\u9084\u662f\u65e5\u5e38\u7684\u6578\u64da\u67e5\u8a62\u4e2d\uff0cCOUNT \u51fd\u6578\u90fd\u626e\u6f14\u8457\u4e0d\u53ef\u6216\u7f3a\u7684\u89d2\u8272\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e COUNT \u64cd\u4f5c\u7684\u542b\u7fa9\u3001\u4f5c\u7528\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u793a\u4f8b\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-rWImMKsaUR\">COUNT \u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<p>COUNT \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\u8981\u8a08\u7b97\u7684\u5217\u540d\uff0c<code>table_name<\/code> \u662f\u6578\u64da\u8868\u7684\u540d\u7a31\uff0c\u800c <code>condition<\/code> \u5247\u662f\u53ef\u9078\u7684\u904e\u6ffe\u689d\u4ef6\u3002COUNT \u51fd\u6578\u53ef\u4ee5\u7528\u4f86\u8a08\u7b97\u7279\u5b9a\u5217\u4e2d\u975e\u7a7a\u503c\u7684\u6578\u91cf\uff0c\u6216\u8005\u8a08\u7b97\u6574\u500b\u8868\u4e2d\u7684\u884c\u6578\u3002<\/p>\n<h2 id=\"count-%e5%87%bd%e6%95%b8%e7%9a%84%e9%a1%9e%e5%9e%8b-rWImMKsaUR\">COUNT \u51fd\u6578\u7684\u985e\u578b<\/h2>\n<p>COUNT \u51fd\u6578\u4e3b\u8981\u6709\u5169\u7a2e\u4f7f\u7528\u65b9\u5f0f\uff1a<\/p>\n<ul>\n<li><strong>COUNT(*)\uff1a<\/strong>\u8a08\u7b97\u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u5305\u62ec\u7a7a\u503c\u3002<\/li>\n<li><strong>COUNT(column_name)\uff1a<\/strong>\u8a08\u7b97\u6307\u5b9a\u5217\u4e2d\u975e\u7a7a\u503c\u7684\u6578\u91cf\u3002<\/li>\n<\/ul>\n<p>\u4f8b\u5982\uff0c\u5047\u8a2d\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8868\uff0c\u5305\u542b\u54e1\u5de5\u7684\u8cc7\u6599\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<pre><code>SELECT COUNT(*) FROM employees;<\/code><\/pre>\n<p>\u5982\u679c\u6211\u5011\u53ea\u60f3\u8a08\u7b97\u6709\u85aa\u6c34\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\uff1a<\/p>\n<pre><code>SELECT COUNT(salary) FROM employees;<\/code><\/pre>\n<h2 id=\"count-%e5%87%bd%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8%e5%a0%b4%e6%99%af-rWImMKsaUR\">COUNT \u51fd\u6578\u7684\u61c9\u7528\u5834\u666f<\/h2>\n<p>COUNT \u51fd\u6578\u5728\u591a\u7a2e\u5834\u666f\u4e2d\u90fd\u975e\u5e38\u6709\u7528\uff0c\u4ee5\u4e0b\u662f\u4e00\u4e9b\u5e38\u898b\u7684\u61c9\u7528\u5834\u666f\uff1a<\/p>\n<h3 id=\"1-%e6%95%b8%e6%93%9a%e5%88%86%e6%9e%90-rWImMKsaUR\">1. \u6578\u64da\u5206\u6790<\/h3>\n<p>\u5728\u6578\u64da\u5206\u6790\u4e2d\uff0cCOUNT \u51fd\u6578\u53ef\u4ee5\u5e6b\u52a9\u5206\u6790\u5e2b\u5feb\u901f\u4e86\u89e3\u6578\u64da\u7684\u5206\u4f48\u60c5\u6cc1\u3002\u4f8b\u5982\uff0c\u5206\u6790\u67d0\u500b\u7522\u54c1\u7684\u92b7\u552e\u6578\u91cf\uff0c\u6216\u8005\u67d0\u500b\u5730\u5340\u7684\u5ba2\u6236\u6578\u91cf\u3002<\/p>\n<h3 id=\"2-%e5%a0%b1%e5%91%8a%e7%94%9f%e6%88%90-rWImMKsaUR\">2. \u5831\u544a\u751f\u6210<\/h3>\n<p>\u5728\u751f\u6210\u5831\u544a\u6642\uff0cCOUNT \u51fd\u6578\u53ef\u4ee5\u7528\u4f86\u63d0\u4f9b\u95dc\u9375\u6307\u6a19\uff0c\u5982\u7528\u6236\u8a3b\u518a\u6578\u91cf\u3001\u8a02\u55ae\u6578\u91cf\u7b49\uff0c\u9019\u4e9b\u6307\u6a19\u5c0d\u65bc\u696d\u52d9\u6c7a\u7b56\u81f3\u95dc\u91cd\u8981\u3002<\/p>\n<h3 id=\"3-%e6%95%b8%e6%93%9a%e5%ae%8c%e6%95%b4%e6%80%a7%e6%aa%a2%e6%9f%a5-rWImMKsaUR\">3. \u6578\u64da\u5b8c\u6574\u6027\u6aa2\u67e5<\/h3>\n<p>COUNT \u51fd\u6578\u9084\u53ef\u4ee5\u7528\u4f86\u6aa2\u67e5\u6578\u64da\u7684\u5b8c\u6574\u6027\u3002\u4f8b\u5982\uff0c\u901a\u904e\u8a08\u7b97\u67d0\u500b\u8868\u4e2d\u7684\u884c\u6578\uff0c\u53ef\u4ee5\u78ba\u4fdd\u6578\u64da\u5728\u5c0e\u5165\u6216\u66f4\u65b0\u904e\u7a0b\u4e2d\u6c92\u6709\u4e1f\u5931\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8-count-%e5%87%bd%e6%95%b8%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-rWImMKsaUR\">\u4f7f\u7528 COUNT \u51fd\u6578\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u4f7f\u7528 COUNT \u51fd\u6578\u6642\uff0c\u6709\u5e7e\u9ede\u9700\u8981\u6ce8\u610f\uff1a<\/p>\n<ul>\n<li>COUNT(*) \u8a08\u7b97\u6240\u6709\u884c\uff0c\u5305\u62ec\u7a7a\u503c\uff0c\u800c COUNT(column_name) \u53ea\u8a08\u7b97\u975e\u7a7a\u503c\u3002<\/li>\n<li>\u5728\u4f7f\u7528 GROUP BY \u5b50\u53e5\u6642\uff0cCOUNT \u51fd\u6578\u53ef\u4ee5\u8207\u5176\u4ed6\u805a\u5408\u51fd\u6578\u4e00\u8d77\u4f7f\u7528\uff0c\u4ee5\u7372\u5f97\u66f4\u8a73\u7d30\u7684\u6578\u64da\u5206\u6790\u3002<\/li>\n<li>\u904e\u6ffe\u689d\u4ef6\u53ef\u4ee5\u901a\u904e WHERE \u5b50\u53e5\u4f86\u6307\u5b9a\uff0c\u4ee5\u4fbf\u53ea\u8a08\u7b97\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u884c\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b5%90%e8%ab%96-rWImMKsaUR\">\u7d50\u8ad6<\/h2>\n<p>COUNT \u51fd\u6578\u5728\u6578\u64da\u5eab\u64cd\u4f5c\u4e2d\u5177\u6709\u91cd\u8981\u7684\u610f\u7fa9\u548c\u4f5c\u7528\u3002\u5b83\u4e0d\u50c5\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u7372\u53d6\u6578\u64da\u7684\u57fa\u672c\u7d71\u8a08\u4fe1\u606f\uff0c\u9084\u80fd\u5728\u6578\u64da\u5206\u6790\u548c\u5831\u544a\u751f\u6210\u4e2d\u767c\u63ee\u95dc\u9375\u4f5c\u7528\u3002\u7121\u8ad6\u662f\u5728\u65e5\u5e38\u7684\u6578\u64da\u67e5\u8a62\u9084\u662f\u8907\u96dc\u7684\u6578\u64da\u5206\u6790\u4e2d\uff0c\u638c\u63e1 COUNT \u51fd\u6578\u7684\u4f7f\u7528\u90fd\u662f\u975e\u5e38\u5fc5\u8981\u7684\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u64cd\u4f5c\u6709\u9032\u4e00\u6b65\u7684\u9700\u6c42\uff0c\u6216\u8005\u9700\u8981\u9ad8\u6548\u7684 <a href=\"https:\/\/server.hk\">VPS<\/a> \u89e3\u6c7a\u65b9\u6848\u4f86\u652f\u6301\u60a8\u7684\u696d\u52d9\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4ee5\u7372\u53d6\u66f4\u591a\u4fe1\u606f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u6df1\u5165\u4e86\u89e3\u6578\u64da\u5eab\u4e2dcount\u64cd\u4f5c\u7684\u542b\u7fa9\u8207\u4f5c\u7528\uff0c\u63a2\u7d22\u5176\u5728\u6578\u64da\u7d71\u8a08\u548c\u67e5\u8a62\u4e2d\u7684\u91cd\u8981\u6027\u8207\u61c9\u7528\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-180896","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/180896","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=180896"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/180896\/revisions"}],"predecessor-version":[{"id":180897,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/180896\/revisions\/180897"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=180896"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=180896"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=180896"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}