{"id":185304,"date":"2024-11-10T20:27:00","date_gmt":"2024-11-10T12:27:00","guid":{"rendered":"https:\/\/server.hk\/cnblog\/185304\/"},"modified":"2024-11-10T20:27:01","modified_gmt":"2024-11-10T12:27:01","slug":"%e4%bd%bf%e7%94%a8sql%e4%b8%adcount%e5%87%bd%e6%95%b8%e5%b0%8d%e4%b8%80%e5%88%97%e4%b8%ad%e6%95%b8%e6%93%9a%e8%a8%88%e6%95%b8%e7%9a%84%e5%af%a6%e4%be%8b","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/185304\/","title":{"rendered":"\u4f7f\u7528SQL\u4e2dCOUNT()\u51fd\u6578\u5c0d\u4e00\u5217\u4e2d\u6578\u64da\u8a08\u6578\u7684\u5be6\u4f8b"},"content":{"rendered":"<h1 id=\"%e4%bd%bf%e7%94%a8sql%e4%b8%adcount%e5%87%bd%e6%95%b8%e5%b0%8d%e4%b8%80%e5%88%97%e4%b8%ad%e6%95%b8%e6%93%9a%e8%a8%88%e6%95%b8%e7%9a%84%e5%af%a6%e4%be%8b-BEHawRmlKr\">\u4f7f\u7528SQL\u4e2dCOUNT()\u51fd\u6578\u5c0d\u4e00\u5217\u4e2d\u6578\u64da\u8a08\u6578\u7684\u5be6\u4f8b<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cSQL\uff08\u7d50\u69cb\u5316\u67e5\u8a62\u8a9e\u8a00\uff09\u662f\u4e00\u7a2e\u975e\u5e38\u91cd\u8981\u7684\u5de5\u5177\u3002\u5b83\u5141\u8a31\u7528\u6236\u5c0d\u6578\u64da\u9032\u884c\u67e5\u8a62\u3001\u66f4\u65b0\u548c\u7ba1\u7406\u3002\u5176\u4e2d\uff0c<code>COUNT()<\/code> \u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u6709\u7528\u7684\u805a\u5408\u51fd\u6578\uff0c\u80fd\u5920\u8a08\u7b97\u4e00\u5217\u4e2d\u7b26\u5408\u7279\u5b9a\u689d\u4ef6\u7684\u6578\u64da\u884c\u6578\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0e <code>COUNT()<\/code> \u51fd\u6578\u7684\u7528\u6cd5\uff0c\u4e26\u63d0\u4f9b\u4e00\u4e9b\u5be6\u969b\u7684\u4f8b\u5b50\u4f86\u5e6b\u52a9\u8b80\u8005\u66f4\u597d\u5730\u7406\u89e3\u5176\u61c9\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-BEHawRmlKr\">COUNT() \u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5<\/h2>\n<p><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\u6578\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\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-BEHawRmlKr\">COUNT() \u51fd\u6578\u7684\u4f7f\u7528\u793a\u4f8b<\/h2>\n<h3 id=\"%e7%a4%ba%e4%be%8b-1%ef%bc%9a%e8%a8%88%e7%ae%97%e6%89%80%e6%9c%89%e8%a1%8c%e7%9a%84%e6%95%b8%e9%87%8f-BEHawRmlKr\">\u793a\u4f8b 1\uff1a\u8a08\u7b97\u6240\u6709\u884c\u7684\u6578\u91cf<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8868\uff0c\u8a72\u8868\u5305\u542b\u6240\u6709\u54e1\u5de5\u7684\u8cc7\u6599\u3002\u6211\u5011\u60f3\u8981\u8a08\u7b97\u8868\u4e2d\u6240\u6709\u54e1\u5de5\u7684\u7e3d\u6578\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM employees;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de <code>employees<\/code> \u8868\u4e2d\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u5305\u62ec\u6240\u6709\u7684\u54e1\u5de5\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b-2%ef%bc%9a%e8%a8%88%e7%ae%97%e7%89%b9%e5%ae%9a%e6%a2%9d%e4%bb%b6%e4%b8%8b%e7%9a%84%e8%a1%8c%e6%95%b8-BEHawRmlKr\">\u793a\u4f8b 2\uff1a\u8a08\u7b97\u7279\u5b9a\u689d\u4ef6\u4e0b\u7684\u884c\u6578<\/h3>\n<p>\u5982\u679c\u6211\u5011\u53ea\u60f3\u8a08\u7b97\u5728\u67d0\u500b\u90e8\u9580\u5de5\u4f5c\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u4f8b\u5982\u300c\u92b7\u552e\u90e8\u300d\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT COUNT(*) FROM employees WHERE department = 'Sales';<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u6240\u6709\u5728\u300c\u92b7\u552e\u90e8\u300d\u5de5\u4f5c\u7684\u54e1\u5de5\u7684\u6578\u91cf\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b-3%ef%bc%9a%e8%a8%88%e7%ae%97%e4%b8%8d%e9%87%8d%e8%a4%87%e7%9a%84%e5%80%bc-BEHawRmlKr\">\u793a\u4f8b 3\uff1a\u8a08\u7b97\u4e0d\u91cd\u8907\u7684\u503c<\/h3>\n<p>\u6709\u6642\u5019\uff0c\u6211\u5011\u53ef\u80fd\u9700\u8981\u8a08\u7b97\u67d0\u4e00\u5217\u4e2d\u4e0d\u91cd\u8907\u7684\u503c\u7684\u6578\u91cf\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6211\u5011\u60f3\u77e5\u9053\u6709\u591a\u5c11\u500b\u4e0d\u540c\u7684\u8077\u4f4d\uff0c\u53ef\u4ee5\u4f7f\u7528 <code>DISTINCT<\/code> \u95dc\u9375\u5b57\uff1a<\/p>\n<pre><code>SELECT COUNT(DISTINCT job_title) FROM employees;<\/code><\/pre>\n<p>\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de <code>employees<\/code> \u8868\u4e2d\u4e0d\u540c\u8077\u4f4d\u7684\u6578\u91cf\u3002<\/p>\n<h2 id=\"count-%e5%87%bd%e6%95%b8%e7%9a%84%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-BEHawRmlKr\">COUNT() \u51fd\u6578\u7684\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li><strong>NULL \u503c\uff1a<\/strong> <code>COUNT(column_name)<\/code> \u4e0d\u6703\u8a08\u7b97 <code>NULL<\/code> \u503c\uff0c\u800c <code>COUNT(*)<\/code> \u6703\u8a08\u7b97\u6240\u6709\u884c\uff0c\u5305\u62ec <code>NULL<\/code> \u503c\u3002<\/li>\n<li><strong>\u6027\u80fd\u8003\u91cf\uff1a<\/strong> \u5728\u5927\u578b\u6578\u64da\u96c6\u4e0a\u4f7f\u7528 <code>COUNT()<\/code> \u51fd\u6578\u6642\uff0c\u53ef\u80fd\u6703\u5f71\u97ff\u67e5\u8a62\u6027\u80fd\uff0c\u56e0\u6b64\u5728\u8a2d\u8a08\u6578\u64da\u5eab\u6642\u61c9\u8003\u616e\u7d22\u5f15\u7684\u4f7f\u7528\u3002<\/li>\n<li><strong>\u805a\u5408\u51fd\u6578\uff1a<\/strong> <code>COUNT()<\/code> \u662f\u4e00\u7a2e\u805a\u5408\u51fd\u6578\uff0c\u901a\u5e38\u8207 <code>GROUP BY<\/code> \u5b50\u53e5\u4e00\u8d77\u4f7f\u7528\uff0c\u4ee5\u4fbf\u5c0d\u5206\u7d44\u6578\u64da\u9032\u884c\u8a08\u6578\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b5%90%e8%ab%96-BEHawRmlKr\">\u7d50\u8ad6<\/h2>\n<p>\u5728\u672c\u6587\u4e2d\uff0c\u6211\u5011\u63a2\u8a0e\u4e86 SQL \u4e2d <code>COUNT()<\/code> \u51fd\u6578\u7684\u57fa\u672c\u7528\u6cd5\u53ca\u5176\u591a\u7a2e\u61c9\u7528\u793a\u4f8b\u3002\u7121\u8ad6\u662f\u8a08\u7b97\u6240\u6709\u884c\u7684\u6578\u91cf\u3001\u7279\u5b9a\u689d\u4ef6\u4e0b\u7684\u884c\u6578\uff0c\u9084\u662f\u8a08\u7b97\u4e0d\u91cd\u8907\u7684\u503c\uff0c<code>COUNT()<\/code> \u51fd\u6578\u90fd\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u66f4\u597d\u5730\u5206\u6790\u548c\u7ba1\u7406\u6578\u64da\u3002<\/p>\n<p>\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u76f8\u95dc\u6280\u8853\u6709\u8208\u8da3\uff0c\u4e26\u5e0c\u671b\u7372\u5f97\u66f4\u591a\u8cc7\u8a0a\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9 <a href=\"https:\/\/server.hk\">Server.HK<\/a>\uff0c\u4e86\u89e3\u66f4\u591a\u6709\u95dc <a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a> \u548c <a href=\"https:\/\/server.hk\">\u96f2\u4f3a\u670d\u5668<\/a> \u7684\u8cc7\u8a0a\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3\u5982\u4f55\u5728SQL\u4e2d\u4f7f\u7528COUNT()\u51fd\u6578\u5c0d\u4e00\u5217\u6578\u64da\u9032\u884c\u8a08\u6578<\/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-185304","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/185304","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=185304"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/185304\/revisions"}],"predecessor-version":[{"id":185305,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/185304\/revisions\/185305"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=185304"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=185304"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=185304"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}