{"id":217813,"date":"2023-12-23T00:41:26","date_gmt":"2023-12-22T16:41:26","guid":{"rendered":"https:\/\/www.idc.net\/help\/217813\/"},"modified":"2023-12-23T00:41:26","modified_gmt":"2023-12-22T16:41:26","slug":"mysql%e4%bd%bf%e7%94%a8%e6%89%8b%e5%86%8c%ef%bc%9a%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b0%e8%bf%94%e5%9b%9e%e7%ac%a6%e5%90%88%e7%89%b9%e5%ae%9a%e6%9d%a1%e4%bb%b6%e7%9a%84%e8%a1%8c%e6%95%b0","status":"publish","type":"post","link":"https:\/\/idc.net\/help\/217813\/","title":{"rendered":"MySQL\u4f7f\u7528\u624b\u518c\uff1a\u4f7f\u7528COUNT()\u51fd\u6570\u8fd4\u56de\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570"},"content":{"rendered":"<p><title id=\"mysql%e4%bd%bf%e7%94%a8%e6%89%8b%e5%86%8c%ef%bc%9a%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b0%e8%bf%94%e5%9b%9e%e7%ac%a6%e5%90%88%e7%89%b9%e5%ae%9a%e6%9d%a1%e4%bb%b6%e7%9a%84%e8%a1%8c%e6%95%b0-XTsjWLwlXj\">MySQL\u4f7f\u7528\u624b\u518c\uff1a\u4f7f\u7528COUNT()\u51fd\u6570\u8fd4\u56de\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570<\/title><\/p>\n<h1 id=\"mysql%e4%bd%bf%e7%94%a8%e6%89%8b%e5%86%8c%ef%bc%9a%e4%bd%bf%e7%94%a8count%e5%87%bd%e6%95%b0%e8%bf%94%e5%9b%9e%e7%ac%a6%e5%90%88%e7%89%b9%e5%ae%9a%e6%9d%a1%e4%bb%b6%e7%9a%84%e8%a1%8c%e6%95%b0-XTsjWLwlXj\">MySQL\u4f7f\u7528\u624b\u518c\uff1a\u4f7f\u7528COUNT()\u51fd\u6570\u8fd4\u56de\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570<\/h1>\n<p>\u5728MySQL\u4e2d\uff0cCOUNT()\u51fd\u6570\u662f\u4e00\u4e2a\u975e\u5e38\u6709\u7528\u7684\u51fd\u6570\uff0c\u5b83\u53ef\u4ee5\u7528\u6765\u8fd4\u56de\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570\u3002\u65e0\u8bba\u662f\u5728\u6570\u636e\u5206\u6790\u3001\u62a5\u8868\u751f\u6210\u8fd8\u662f\u67e5\u8be2\u4f18\u5316\u4e2d\uff0cCOUNT()\u51fd\u6570\u90fd\u626e\u6f14\u7740\u91cd\u8981\u7684\u89d2\u8272\u3002<\/p>\n<h2 id=\"%e8%af%ad%e6%b3%95-XTsjWLwlXj\">\u8bed\u6cd5<\/h2>\n<p>COUNT()\u51fd\u6570\u7684\u57fa\u672c\u8bed\u6cd5\u5982\u4e0b\uff1a<\/p>\n<pre><code>COUNT(expression)\n<\/code><\/pre>\n<p>\u5176\u4e2d\uff0cexpression\u662f\u4e00\u4e2a\u8868\u8fbe\u5f0f\uff0c\u53ef\u4ee5\u662f\u5217\u540d\u3001\u5e38\u91cf\u6216\u8005\u51fd\u6570\u3002COUNT()\u51fd\u6570\u4f1a\u8fd4\u56deexpression\u7684\u975eNULL\u503c\u7684\u6570\u91cf\u3002<\/p>\n<h2 id=\"%e7%a4%ba%e4%be%8b-XTsjWLwlXj\">\u793a\u4f8b<\/h2>\n<p>\u5047\u8bbe\u6211\u4eec\u6709\u4e00\u4e2a\u540d\u4e3a\"users\"\u7684\u8868\uff0c\u5176\u4e2d\u5305\u542b\u4e86\u7528\u6237\u7684\u4fe1\u606f\u3002\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528COUNT()\u51fd\u6570\u6765\u7edf\u8ba1\u8868\u4e2d\u7684\u7528\u6237\u6570\u91cf\u3002<\/p>\n<pre><code>SELECT COUNT(*) FROM users;\n<\/code><\/pre>\n<p>\u4e0a\u8ff0\u67e5\u8be2\u5c06\u8fd4\u56de\"users\"\u8868\u4e2d\u7684\u603b\u884c\u6570\u3002<\/p>\n<p>\u9664\u4e86\u7edf\u8ba1\u603b\u884c\u6570\uff0c\u6211\u4eec\u8fd8\u53ef\u4ee5\u6839\u636e\u7279\u5b9a\u6761\u4ef6\u6765\u7edf\u8ba1\u7b26\u5408\u6761\u4ef6\u7684\u884c\u6570\u3002\u4f8b\u5982\uff0c\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528COUNT()\u51fd\u6570\u6765\u7edf\u8ba1\u5e74\u9f84\u5927\u4e8e\u7b49\u4e8e18\u5c81\u7684\u7528\u6237\u6570\u91cf\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM users WHERE age &gt;= 18;\n<\/code><\/pre>\n<p>\u4e0a\u8ff0\u67e5\u8be2\u5c06\u8fd4\u56de\"users\"\u8868\u4e2d\u5e74\u9f84\u5927\u4e8e\u7b49\u4e8e18\u5c81\u7684\u7528\u6237\u6570\u91cf\u3002<\/p>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a1%b9-XTsjWLwlXj\">\u6ce8\u610f\u4e8b\u9879<\/h2>\n<p>\u5728\u4f7f\u7528COUNT()\u51fd\u6570\u65f6\uff0c\u9700\u8981\u6ce8\u610f\u4ee5\u4e0b\u51e0\u70b9\uff1a<\/p>\n<ul>\n<li>COUNT()\u51fd\u6570\u53ea\u4f1a\u7edf\u8ba1\u975eNULL\u503c\u7684\u6570\u91cf\u3002<\/li>\n<li>COUNT()\u51fd\u6570\u53ef\u4ee5\u7528\u4e8e\u4efb\u4f55\u6570\u636e\u7c7b\u578b\u7684\u5217\u3002<\/li>\n<li>COUNT()\u51fd\u6570\u53ef\u4ee5\u4e0e\u5176\u4ed6\u51fd\u6570\u4e00\u8d77\u4f7f\u7528\uff0c\u4f8b\u5982SUM()\u3001AVG()\u7b49\u3002<\/li>\n<\/ul>\n<h2 id=\"%e6%80%bb%e7%bb%93-XTsjWLwlXj\">\u603b\u7ed3<\/h2>\n<p>\u901a\u8fc7\u672c\u6587\uff0c\u6211\u4eec\u4e86\u89e3\u4e86MySQL\u4e2dCOUNT()\u51fd\u6570\u7684\u7528\u6cd5\u3002COUNT()\u51fd\u6570\u53ef\u4ee5\u7528\u6765\u7edf\u8ba1\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570\uff0c\u65e0\u8bba\u662f\u5728\u6570\u636e\u5206\u6790\u3001\u62a5\u8868\u751f\u6210\u8fd8\u662f\u67e5\u8be2\u4f18\u5316\u4e2d\uff0c\u90fd\u975e\u5e38\u6709\u7528\u3002<\/p>\n<p>\u5982\u679c\u60a8\u60f3\u4e86\u89e3\u66f4\u591a\u5173\u4e8eMySQL\u7684\u4f7f\u7528\u624b\u518c\uff0c\u8bf7\u8bbf\u95ee\u6211\u4eec\u7684\u5b98\u7f51\uff1a<a href=\"https:\/\/idc.net\">https:\/\/idc.net<\/a>\u3002\u6211\u4eec\u63d0\u4f9b\u9999\u6e2f\u670d\u52a1\u5668\u3001\u7f8e\u56fd\u670d\u52a1\u5668\u548c\u4e91\u670d\u52a1\u5668\u7b49\u4ea7\u54c1\uff0c\u4e3a\u60a8\u63d0\u4f9b\u7a33\u5b9a\u53ef\u9760\u7684\u4e91\u8ba1\u7b97\u670d\u52a1\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>MySQL\u4f7f\u7528\u624b\u518c\uff1a\u4f7f\u7528COUNT()\u51fd\u6570\u8fd4\u56de\u7b26\u5408\u7279\u5b9a\u6761\u4ef6\u7684\u884c\u6570 MySQL\u4f7f\u7528\u624b\u518c\uff1a\u4f7f\u7528COUNT()\u51fd\u6570\u8fd4 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[197851],"tags":[],"class_list":["post-217813","post","type-post","status-publish","format-standard","hentry","category-php"],"_links":{"self":[{"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/posts\/217813","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/comments?post=217813"}],"version-history":[{"count":0,"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/posts\/217813\/revisions"}],"wp:attachment":[{"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/media?parent=217813"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/categories?post=217813"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/idc.net\/help\/wp-json\/wp\/v2\/tags?post=217813"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}