{"id":77704,"date":"2024-10-16T11:04:37","date_gmt":"2024-10-16T03:04:37","guid":{"rendered":"https:\/\/server.hk\/cnblog\/77704\/"},"modified":"2024-10-16T11:04:37","modified_gmt":"2024-10-16T03:04:37","slug":"mysql%e6%8c%87%e4%bb%a4-avg%ef%bc%88%e5%b9%b3%e5%9d%87%e5%80%bc%ef%bc%89","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/77704\/","title":{"rendered":"MySQL\u6307\u4ee4: AVG()\uff08\u5e73\u5747\u503c\uff09"},"content":{"rendered":"<h1 id=\"mysql%e6%8c%87%e4%bb%a4-avg%ef%bc%88%e5%b9%b3%e5%9d%87%e5%80%bc%ef%bc%89-ekYVqeXFJd\">MySQL\u6307\u4ee4: AVG()\uff08\u5e73\u5747\u503c\uff09<\/h1>\n<p>\u5728\u6578\u64da\u5eab\u7ba1\u7406\u4e2d\uff0cMySQL\u662f\u4e00\u500b\u5ee3\u6cdb\u4f7f\u7528\u7684\u95dc\u806f\u6578\u64da\u5eab\u7ba1\u7406\u7cfb\u7d71\u3002\u5b83\u63d0\u4f9b\u4e86\u591a\u7a2e\u529f\u80fd\u4f86\u8655\u7406\u548c\u5206\u6790\u6578\u64da\uff0c\u5176\u4e2d\u4e4b\u4e00\u5c31\u662f\u8a08\u7b97\u5e73\u5747\u503c\u7684AVG()\u51fd\u6578\u3002\u672c\u6587\u5c07\u6df1\u5165\u63a2\u8a0eAVG()\u51fd\u6578\u7684\u7528\u6cd5\u3001\u8a9e\u6cd5\u53ca\u5176\u5728\u5be6\u969b\u61c9\u7528\u4e2d\u7684\u793a\u4f8b\u3002<\/p>\n<h2 id=\"avg%e5%87%bd%e6%95%b8%e6%a6%82%e8%bf%b0-ekYVqeXFJd\">AVG()\u51fd\u6578\u6982\u8ff0<\/h2>\n<p>AVG()\u51fd\u6578\u662fMySQL\u4e2d\u7684\u805a\u5408\u51fd\u6578\u4e4b\u4e00\uff0c\u7528\u65bc\u8a08\u7b97\u6307\u5b9a\u5217\u7684\u5e73\u5747\u503c\u3002\u9019\u500b\u51fd\u6578\u901a\u5e38\u7528\u65bc\u6578\u5b57\u985e\u578b\u7684\u6578\u64da\uff0c\u4e26\u4e14\u53ef\u4ee5\u8207GROUP BY\u5b50\u53e5\u4e00\u8d77\u4f7f\u7528\uff0c\u4ee5\u4fbf\u5c0d\u5206\u7d44\u6578\u64da\u9032\u884c\u8a08\u7b97\u3002<\/p>\n<h2 id=\"avg%e7%9a%84%e8%aa%9e%e6%b3%95-ekYVqeXFJd\">AVG()\u7684\u8a9e\u6cd5<\/h2>\n<pre><code>AVG([DISTINCT|ALL] expression)<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c<code>expression<\/code>\u662f\u8981\u8a08\u7b97\u5e73\u5747\u503c\u7684\u5217\u540d\u6216\u8a08\u7b97\u5f0f\u3002<code>DISTINCT<\/code>\u95dc\u9375\u5b57\u7528\u65bc\u6392\u9664\u91cd\u8907\u503c\uff0c\u800c<code>ALL<\/code>\u5247\u662f\u9ed8\u8a8d\u9078\u9805\uff0c\u8868\u793a\u8a08\u7b97\u6240\u6709\u503c\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8avg%e7%9a%84%e7%a4%ba%e4%be%8b-ekYVqeXFJd\">\u4f7f\u7528AVG()\u7684\u793a\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u4e9b\u4f7f\u7528AVG()\u51fd\u6578\u7684\u5be6\u969b\u793a\u4f8b\uff1a<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b1-%e8%a8%88%e7%ae%97%e5%96%ae%e4%b8%80%e5%88%97%e7%9a%84%e5%b9%b3%e5%9d%87%e5%80%bc-ekYVqeXFJd\">\u793a\u4f8b1: \u8a08\u7b97\u55ae\u4e00\u5217\u7684\u5e73\u5747\u503c<\/h3>\n<p>\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba<code>students<\/code>\u7684\u8868\u683c\uff0c\u5305\u542b\u5b78\u751f\u7684\u6210\u7e3e\u3002\u8981\u8a08\u7b97\u6240\u6709\u5b78\u751f\u7684\u5e73\u5747\u6210\u7e3e\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u67e5\u8a62\uff1a<\/p>\n<pre><code>SELECT AVG(score) AS average_score FROM students;<\/code><\/pre>\n<p>\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u6240\u6709\u5b78\u751f\u6210\u7e3e\u7684\u5e73\u5747\u503c\uff0c\u4e26\u5c07\u5176\u547d\u540d\u70ba<code>average_score<\/code>\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b2-%e4%bd%bf%e7%94%a8distinct%e8%a8%88%e7%ae%97%e5%94%af%e4%b8%80%e5%80%bc%e7%9a%84%e5%b9%b3%e5%9d%87%e5%80%bc-ekYVqeXFJd\">\u793a\u4f8b2: \u4f7f\u7528DISTINCT\u8a08\u7b97\u552f\u4e00\u503c\u7684\u5e73\u5747\u503c<\/h3>\n<p>\u5982\u679c\u6211\u5011\u5e0c\u671b\u8a08\u7b97\u552f\u4e00\u6210\u7e3e\u7684\u5e73\u5747\u503c\uff0c\u53ef\u4ee5\u4f7f\u7528<code>DISTINCT<\/code>\u95dc\u9375\u5b57\uff1a<\/p>\n<pre><code>SELECT AVG(DISTINCT score) AS average_unique_score FROM students;<\/code><\/pre>\n<p>\u9019\u6a23\u7684\u67e5\u8a62\u5c07\u6392\u9664\u91cd\u8907\u7684\u6210\u7e3e\uff0c\u50c5\u8a08\u7b97\u552f\u4e00\u6210\u7e3e\u7684\u5e73\u5747\u503c\u3002<\/p>\n<h3 id=\"%e7%a4%ba%e4%be%8b3-%e8%88%87group-by%e4%b8%80%e8%b5%b7%e4%bd%bf%e7%94%a8-ekYVqeXFJd\">\u793a\u4f8b3: \u8207GROUP BY\u4e00\u8d77\u4f7f\u7528<\/h3>\n<p>\u7576\u9700\u8981\u6309\u67d0\u500b\u5206\u985e\u9032\u884c\u5e73\u5747\u503c\u8a08\u7b97\u6642\uff0c\u53ef\u4ee5\u4f7f\u7528<code>GROUP BY<\/code>\u5b50\u53e5\u3002\u4f8b\u5982\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b<code>courses<\/code>\u8868\u683c\uff0c\u8a18\u9304\u6bcf\u9580\u8ab2\u7a0b\u7684\u5b78\u751f\u6210\u7e3e\uff0c\u4e26\u5e0c\u671b\u6309\u8ab2\u7a0b\u8a08\u7b97\u5e73\u5747\u6210\u7e3e\uff1a<\/p>\n<pre><code>SELECT course_id, AVG(score) AS average_score \nFROM students \nGROUP BY course_id;<\/code><\/pre>\n<p>\u9019\u689d\u67e5\u8a62\u5c07\u8fd4\u56de\u6bcf\u9580\u8ab2\u7a0b\u7684\u5e73\u5747\u6210\u7e3e\uff0c\u4e26\u6839\u64da<code>course_id<\/code>\u9032\u884c\u5206\u7d44\u3002<\/p>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-ekYVqeXFJd\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<ul>\n<li>AVG()\u51fd\u6578\u50c5\u9069\u7528\u65bc\u6578\u5b57\u985e\u578b\u7684\u6578\u64da\uff0c\u5c0d\u65bc\u5176\u4ed6\u985e\u578b\u7684\u6578\u64da\uff0c\u5c07\u8fd4\u56deNULL\u3002<\/li>\n<li>\u5982\u679c\u8868\u683c\u4e2d\u6c92\u6709\u7b26\u5408\u689d\u4ef6\u7684\u884c\uff0c\u5247AVG()\u5c07\u8fd4\u56deNULL\u3002<\/li>\n<li>\u5728\u4f7f\u7528<code>DISTINCT<\/code>\u6642\uff0c\u8a08\u7b97\u7684\u901f\u5ea6\u53ef\u80fd\u6703\u53d7\u5230\u5f71\u97ff\uff0c\u7279\u5225\u662f\u5728\u5927\u578b\u6578\u64da\u96c6\u4e0a\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b8%bd%e7%b5%90-ekYVqeXFJd\">\u7e3d\u7d50<\/h2>\n<p>AVG()\u51fd\u6578\u5728MySQL\u4e2d\u662f\u4e00\u500b\u5f37\u5927\u7684\u5de5\u5177\uff0c\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u8a08\u7b97\u6578\u64da\u7684\u5e73\u5747\u503c\u3002\u7121\u8ad6\u662f\u55ae\u4e00\u5217\u7684\u8a08\u7b97\uff0c\u9084\u662f\u8207<code>GROUP BY<\/code>\u5b50\u53e5\u7d50\u5408\u4f7f\u7528\uff0cAVG()\u90fd\u80fd\u63d0\u4f9b\u6709\u50f9\u503c\u7684\u6578\u64da\u5206\u6790\u7d50\u679c\u3002\u5c0d\u65bc\u9700\u8981\u9032\u884c\u6578\u64da\u5206\u6790\u7684\u7528\u6236\u4f86\u8aaa\uff0c\u638c\u63e1\u9019\u500b\u51fd\u6578\u7684\u4f7f\u7528\u65b9\u6cd5\u662f\u975e\u5e38\u91cd\u8981\u7684\u3002<\/p>\n<p>\u5982\u679c\u60a8\u6b63\u5728\u5c0b\u627e\u9ad8\u6548\u7684\u6578\u64da\u5eab\u89e3\u6c7a\u65b9\u6848\uff0c\u8003\u616e\u4f7f\u7528\u6211\u5011\u7684<a href=\"https:\/\/server.hk\">\u9999\u6e2fVPS<\/a>\u670d\u52d9\uff0c\u70ba\u60a8\u7684\u61c9\u7528\u63d0\u4f9b\u7a69\u5b9a\u7684\u652f\u6301\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3MySQL\u6307\u4ee4AVG()\uff0c\u7528\u4e8e\u8ba1\u7b97\u6570\u636e\u96c6\u7684\u5e73\u5747\u503c\uff0c\u5e2e\u52a9\u60a8\u8f7b\u677e\u5206\u6790\u548c\u5904\u7406\u6570\u636e\u5e93\u4e2d\u7684\u6570\u503c\u6570\u636e\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-77704","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77704","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=77704"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77704\/revisions"}],"predecessor-version":[{"id":77705,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/77704\/revisions\/77705"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=77704"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=77704"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=77704"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}