{"id":59621,"date":"2024-10-12T23:28:14","date_gmt":"2024-10-12T15:28:14","guid":{"rendered":"https:\/\/server.hk\/cnblog\/59621\/"},"modified":"2024-10-12T23:28:14","modified_gmt":"2024-10-12T15:28:14","slug":"count-%e5%87%bd%e6%95%b8%e5%b0%8d%e5%a4%9a%e5%88%97%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\/59621\/","title":{"rendered":"COUNT( )\u51fd\u6578\u5c0d\u591a\u5217\u6578\u64da\u8a08\u6578\u7684\u5be6\u4f8b"},"content":{"rendered":"

COUNT()\u51fd\u6578\u5c0d\u591a\u5217\u6578\u64da\u8a08\u6578\u7684\u5be6\u4f8b<\/h1>\n

\u5728\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0cCOUNT()<\/code>\u51fd\u6578\u662f\u4e00\u500b\u975e\u5e38\u91cd\u8981\u7684\u805a\u5408\u51fd\u6578\uff0c\u7528\u65bc\u8a08\u7b97\u884c\u6578\u3002\u9019\u500b\u51fd\u6578\u4e0d\u50c5\u53ef\u4ee5\u7528\u4f86\u8a08\u7b97\u55ae\u5217\u7684\u6578\u64da\uff0c\u9084\u53ef\u4ee5\u7528\u65bc\u591a\u5217\u6578\u64da\u7684\u8a08\u6578\u3002\u672c\u6587\u5c07\u63a2\u8a0eCOUNT()<\/code>\u51fd\u6578\u5728\u591a\u5217\u6578\u64da\u8a08\u6578\u4e2d\u7684\u61c9\u7528\uff0c\u4e26\u63d0\u4f9b\u4e00\u4e9b\u5be6\u4f8b\u4f86\u5e6b\u52a9\u7406\u89e3\u3002<\/p>\n

COUNT()\u51fd\u6578\u7684\u57fa\u672c\u7528\u6cd5<\/h2>\n

COUNT()<\/code>\u51fd\u6578\u7684\u57fa\u672c\u8a9e\u6cd5\u5982\u4e0b\uff1a<\/p>\n

SELECT COUNT(column_name) FROM table_name;<\/code><\/pre>\n
\u9019\u500b\u8a9e\u53e5\u5c07\u8fd4\u56de\u6307\u5b9a\u5217\u4e2d\u975e\u7a7a\u503c\u7684\u6578\u91cf\u3002\u5982\u679c\u9700\u8981\u8a08\u7b97\u6240\u6709\u884c\u7684\u6578\u91cf\uff0c\u53ef\u4ee5\u4f7f\u7528\uff1a<\/p>\n
SELECT COUNT(*) FROM table_name;<\/code><\/pre>\n
\u591a\u5217\u8a08\u6578\u7684\u9700\u6c42<\/h2>\n
\u5728\u67d0\u4e9b\u60c5\u6cc1\u4e0b\uff0c\u6211\u5011\u53ef\u80fd\u9700\u8981\u540c\u6642\u8a08\u7b97\u591a\u5217\u7684\u6578\u64da\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70baemployees<\/code>\u7684\u8868\uff0c\u5305\u542b\u4ee5\u4e0b\u5217\uff1adepartment<\/code>\uff08\u90e8\u9580\uff09\u3001salary<\/code>\uff08\u85aa\u6c34\uff09\u548chire_date<\/code>\uff08\u5165\u8077\u65e5\u671f\uff09\u3002\u6211\u5011\u53ef\u80fd\u60f3\u8981\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\u4ee5\u53ca\u4ed6\u5011\u7684\u5e73\u5747\u85aa\u6c34\u3002<\/p>\n
\u4f7f\u7528GROUP BY\u548cCOUNT()\u51fd\u6578<\/h2>\n
\u70ba\u4e86\u5be6\u73fe\u9019\u4e00\u9700\u6c42\uff0c\u6211\u5011\u53ef\u4ee5\u7d50\u5408\u4f7f\u7528GROUP BY<\/code>\u548cCOUNT()<\/code>\u51fd\u6578\u3002\u4ee5\u4e0b\u662f\u4e00\u500b\u793a\u4f8b\u67e5\u8a62\uff1a<\/p>\n
SELECT department, COUNT(*) AS employee_count, AVG(salary) AS average_salary\nFROM employees\nGROUP BY department;<\/code><\/pre>\n
\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\u548c\u5e73\u5747\u85aa\u6c34\u3002GROUP BY<\/code>\u5b50\u53e5\u5c07\u6578\u64da\u6309\u90e8\u9580\u5206\u7d44\uff0c\u800cCOUNT(*)<\/code>\u548cAVG(salary)<\/code>\u5247\u5206\u5225\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\u548c\u5e73\u5747\u85aa\u6c34\u3002<\/p>\n
\u8a08\u7b97\u591a\u5217\u7684\u975e\u7a7a\u503c<\/h2>\n
\u5982\u679c\u6211\u5011\u60f3\u8981\u8a08\u7b97\u591a\u5217\u7684\u975e\u7a7a\u503c\uff0c\u53ef\u4ee5\u4f7f\u7528COUNT()<\/code>\u51fd\u6578\u7684\u591a\u6b21\u8abf\u7528\u3002\u5047\u8a2d\u6211\u5011\u60f3\u8981\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u4e2d\u975e\u7a7a\u85aa\u6c34\u548c\u5165\u8077\u65e5\u671f\u7684\u54e1\u5de5\u6578\u91cf\uff0c\u53ef\u4ee5\u9019\u6a23\u5beb\uff1a<\/p>\n
SELECT department,\n       COUNT(salary) AS non_null_salaries,\n       COUNT(hire_date) AS non_null_hire_dates\nFROM employees\nGROUP BY department;<\/code><\/pre>\n
\u9019\u500b\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u90e8\u9580\u4e2d\u975e\u7a7a\u85aa\u6c34\u548c\u5165\u8077\u65e5\u671f\u7684\u54e1\u5de5\u6578\u91cf\u3002\u9019\u6a23\u7684\u67e5\u8a62\u5c0d\u65bc\u6578\u64da\u5206\u6790\u975e\u5e38\u6709\u7528\uff0c\u56e0\u70ba\u5b83\u53ef\u4ee5\u5e6b\u52a9\u6211\u5011\u4e86\u89e3\u6578\u64da\u7684\u5b8c\u6574\u6027\u3002<\/p>\n
\u7d50\u5408\u5176\u4ed6\u51fd\u6578<\/h2>\n
\u9664\u4e86COUNT()<\/code>\u51fd\u6578\uff0c\u6211\u5011\u9084\u53ef\u4ee5\u7d50\u5408\u5176\u4ed6\u805a\u5408\u51fd\u6578\u4f86\u7372\u53d6\u66f4\u5168\u9762\u7684\u6578\u64da\u3002\u4f8b\u5982\uff0c\u6211\u5011\u53ef\u4ee5\u4f7f\u7528SUM()<\/code>\u51fd\u6578\u4f86\u8a08\u7b97\u6bcf\u500b\u90e8\u9580\u7684\u7e3d\u85aa\u6c34\uff1a<\/p>\n
SELECT department,\n       COUNT(*) AS employee_count,\n       SUM(salary) AS total_salary\nFROM employees\nGROUP BY department;<\/code><\/pre>\n
\u9019\u6a23\u7684\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u500b\u90e8\u9580\u7684\u54e1\u5de5\u6578\u91cf\u548c\u7e3d\u85aa\u6c34\uff0c\u70ba\u7ba1\u7406\u5c64\u63d0\u4f9b\u4e86\u91cd\u8981\u7684\u6c7a\u7b56\u4f9d\u64da\u3002<\/p>\n
\u7e3d\u7d50<\/h2>\n
\u5728\u6578\u64da\u5eab\u4e2d\uff0cCOUNT()<\/code>\u51fd\u6578\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u6211\u5011\u6709\u6548\u5730\u8a08\u7b97\u591a\u5217\u6578\u64da\u3002\u901a\u904e\u7d50\u5408GROUP BY<\/code>\u548c\u5176\u4ed6\u805a\u5408\u51fd\u6578\uff0c\u6211\u5011\u53ef\u4ee5\u7372\u5f97\u66f4\u6df1\u5165\u7684\u6578\u64da\u5206\u6790\u7d50\u679c\u3002\u7121\u8ad6\u662f\u5728\u696d\u52d9\u5831\u544a\u9084\u662f\u6578\u64da\u5206\u6790\u4e2d\uff0c\u638c\u63e1COUNT()<\/code>\u51fd\u6578\u7684\u4f7f\u7528\u90fd\u662f\u975e\u5e38\u91cd\u8981\u7684\u3002<\/p>\n
\u5982\u679c\u60a8\u5c0d\u65bc\u6578\u64da\u5eab\u7ba1\u7406\u6216\u5176\u4ed6\u6280\u8853\u554f\u984c\u6709\u8208\u8da3\uff0c\u6b61\u8fce\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u4e86\u89e3\u66f4\u591a\u8cc7\u8a0a\uff0c\u7279\u5225\u662f\u6211\u5011\u7684VPS<\/a> \u65b9\u6848\uff0c\u80fd\u5920\u70ba\u60a8\u7684\u696d\u52d9\u63d0\u4f9b\u7a69\u5b9a\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u63a2\u7d22COUNT()\u51fd\u6578\u5728\u591a\u5217\u6578\u64da\u8a08\u6578\u4e2d\u7684\u61c9\u7528\u5be6\u4f8b\uff0c\u5b78\u7fd2\u5982\u4f55\u6709\u6548\u7d71\u8a08\u6578\u64da\u4ee5\u63d0\u5347\u5206\u6790\u6548\u7387\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-59621","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/59621","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"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=59621"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/59621\/revisions"}],"predecessor-version":[{"id":59622,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/59621\/revisions\/59622"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=59621"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=59621"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=59621"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}