{"id":143853,"date":"2024-11-01T01:48:20","date_gmt":"2024-10-31T17:48:20","guid":{"rendered":"https:\/\/server.hk\/cnblog\/143853\/"},"modified":"2024-11-01T01:48:21","modified_gmt":"2024-10-31T17:48:21","slug":"sql-%e8%81%9a%e5%90%88%e5%87%bd%e6%95%b8%e4%b9%8b-avg-%e5%87%bd%e6%95%b8","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/143853\/","title":{"rendered":"SQL \u805a\u5408\u51fd\u6578\u4e4b Avg \u51fd\u6578"},"content":{"rendered":"<h1 id=\"sql-%e8%81%9a%e5%90%88%e5%87%bd%e6%95%b8%e4%b9%8b-avg-%e5%87%bd%e6%95%b8-poiGhWdFtf\">SQL \u805a\u5408\u51fd\u6578\u4e4b Avg \u51fd\u6578<\/h1>\n<p>\u5728\u8cc7\u6599\u5eab\u7ba1\u7406\u7cfb\u7d71\u4e2d\uff0cSQL\uff08\u7d50\u69cb\u5316\u67e5\u8a62\u8a9e\u8a00\uff09\u662f\u4e00\u7a2e\u7528\u65bc\u67e5\u8a62\u548c\u64cd\u4f5c\u8cc7\u6599\u7684\u6a19\u6e96\u8a9e\u8a00\u3002\u805a\u5408\u51fd\u6578\u662f SQL \u4e2d\u7684\u4e00\u500b\u91cd\u8981\u6982\u5ff5\uff0c\u9019\u4e9b\u51fd\u6578\u80fd\u5920\u5c0d\u4e00\u7d44\u503c\u9032\u884c\u8a08\u7b97\u4e26\u8fd4\u56de\u55ae\u4e00\u7684\u503c\u3002\u672c\u6587\u5c07\u91cd\u9ede\u4ecb\u7d39 SQL \u4e2d\u7684 Avg \u51fd\u6578\uff0c\u9019\u662f\u4e00\u500b\u7528\u65bc\u8a08\u7b97\u6578\u503c\u578b\u8cc7\u6599\u5e73\u5747\u503c\u7684\u805a\u5408\u51fd\u6578\u3002<\/p>\n<h2 id=\"avg-%e5%87%bd%e6%95%b8%e7%9a%84%e5%9f%ba%e6%9c%ac%e6%a6%82%e5%bf%b5-poiGhWdFtf\">Avg \u51fd\u6578\u7684\u57fa\u672c\u6982\u5ff5<\/h2>\n<p>Avg \u51fd\u6578\u7684\u5168\u540d\u662f Average \u51fd\u6578\uff0c\u4e3b\u8981\u7528\u65bc\u8a08\u7b97\u6307\u5b9a\u6b04\u4f4d\u4e2d\u6240\u6709\u6578\u503c\u7684\u5e73\u5747\u503c\u3002\u9019\u500b\u51fd\u6578\u5728\u6578\u64da\u5206\u6790\u4e2d\u975e\u5e38\u6709\u7528\uff0c\u56e0\u70ba\u5b83\u80fd\u5920\u5e6b\u52a9\u7528\u6236\u5feb\u901f\u4e86\u89e3\u6578\u64da\u7684\u6574\u9ad4\u8da8\u52e2\u3002<\/p>\n<h3 id=\"avg-%e5%87%bd%e6%95%b8%e7%9a%84%e8%aa%9e%e6%b3%95-poiGhWdFtf\">Avg \u51fd\u6578\u7684\u8a9e\u6cd5<\/h3>\n<pre><code>AVG(expression)<\/code><\/pre>\n<p>\u5728\u9019\u88e1\uff0c<code>expression<\/code> \u662f\u4e00\u500b\u6578\u503c\u578b\u7684\u6b04\u4f4d\u6216\u8a08\u7b97\u7d50\u679c\u3002Avg \u51fd\u6578\u6703\u5ffd\u7565 NULL \u503c\uff0c\u56e0\u6b64\u5728\u8a08\u7b97\u5e73\u5747\u503c\u6642\uff0c\u53ea\u6709\u975e NULL \u7684\u6578\u503c\u6703\u88ab\u8003\u616e\u3002<\/p>\n<h2 id=\"%e4%bd%bf%e7%94%a8-avg-%e5%87%bd%e6%95%b8%e7%9a%84%e7%af%84%e4%be%8b-poiGhWdFtf\">\u4f7f\u7528 Avg \u51fd\u6578\u7684\u7bc4\u4f8b<\/h2>\n<p>\u4ee5\u4e0b\u662f\u4e00\u500b\u4f7f\u7528 Avg \u51fd\u6578\u7684\u7bc4\u4f8b\uff0c\u5047\u8a2d\u6211\u5011\u6709\u4e00\u500b\u540d\u70ba <code>employees<\/code> \u7684\u8cc7\u6599\u8868\uff0c\u8a72\u8868\u5305\u542b\u54e1\u5de5\u7684\u85aa\u8cc7\u8cc7\u8a0a\uff1a<\/p>\n<pre><code>CREATE TABLE employees (\n    id INT PRIMARY KEY,\n    name VARCHAR(100),\n    salary DECIMAL(10, 2)\n);\n\nINSERT INTO employees (id, name, salary) VALUES\n(1, 'Alice', 50000),\n(2, 'Bob', 60000),\n(3, 'Charlie', NULL),\n(4, 'David', 70000);\n<\/code><\/pre>\n<p>\u5728\u9019\u500b\u7bc4\u4f8b\u4e2d\uff0c\u6211\u5011\u53ef\u4ee5\u4f7f\u7528 Avg \u51fd\u6578\u4f86\u8a08\u7b97\u6240\u6709\u54e1\u5de5\u7684\u5e73\u5747\u85aa\u8cc7\uff1a<\/p>\n<pre><code>SELECT AVG(salary) AS average_salary FROM employees;\n<\/code><\/pre>\n<p>\u57f7\u884c\u4e0a\u8ff0\u67e5\u8a62\u5f8c\uff0c\u7d50\u679c\u5c07\u8fd4\u56de\u6240\u6709\u975e NULL \u85aa\u8cc7\u7684\u5e73\u5747\u503c\u3002\u5728\u9019\u500b\u4f8b\u5b50\u4e2d\uff0c\u5e73\u5747\u85aa\u8cc7\u5c07\u662f (50000 + 60000 + 70000) \/ 3 = 60000\u3002<\/p>\n<h2 id=\"avg-%e5%87%bd%e6%95%b8%e7%9a%84%e6%87%89%e7%94%a8%e5%a0%b4%e6%99%af-poiGhWdFtf\">Avg \u51fd\u6578\u7684\u61c9\u7528\u5834\u666f<\/h2>\n<p>Avg \u51fd\u6578\u5728\u8a31\u591a\u5834\u666f\u4e2d\u90fd\u975e\u5e38\u6709\u7528\uff0c\u4f8b\u5982\uff1a<\/p>\n<ul>\n<li><strong>\u696d\u52d9\u5831\u544a\uff1a<\/strong>\u4f01\u696d\u53ef\u4ee5\u4f7f\u7528 Avg \u51fd\u6578\u4f86\u8a08\u7b97\u92b7\u552e\u984d\u3001\u6210\u672c\u6216\u5176\u4ed6\u95dc\u9375\u6307\u6a19\u7684\u5e73\u5747\u503c\uff0c\u4ee5\u4fbf\u9032\u884c\u696d\u52d9\u5206\u6790\u3002<\/li>\n<li><strong>\u5b78\u8853\u7814\u7a76\uff1a<\/strong>\u5728\u5b78\u8853\u7814\u7a76\u4e2d\uff0c\u7814\u7a76\u4eba\u54e1\u53ef\u4ee5\u5229\u7528 Avg \u51fd\u6578\u4f86\u5206\u6790\u5be6\u9a57\u6578\u64da\uff0c\u8a08\u7b97\u6a23\u672c\u7684\u5e73\u5747\u503c\u3002<\/li>\n<li><strong>\u8ca1\u52d9\u5206\u6790\uff1a<\/strong>\u8ca1\u52d9\u5206\u6790\u5e2b\u53ef\u4ee5\u4f7f\u7528 Avg \u51fd\u6578\u4f86\u8a08\u7b97\u6295\u8cc7\u56de\u5831\u7387\u7684\u5e73\u5747\u503c\uff0c\u5e6b\u52a9\u505a\u51fa\u66f4\u660e\u667a\u7684\u6295\u8cc7\u6c7a\u7b56\u3002<\/li>\n<\/ul>\n<h2 id=\"%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a0%85-poiGhWdFtf\">\u6ce8\u610f\u4e8b\u9805<\/h2>\n<p>\u5728\u4f7f\u7528 Avg \u51fd\u6578\u6642\uff0c\u6709\u5e7e\u9ede\u9700\u8981\u6ce8\u610f\uff1a<\/p>\n<ul>\n<li>Avg \u51fd\u6578\u53ea\u9069\u7528\u65bc\u6578\u503c\u578b\u8cc7\u6599\uff0c\u5c0d\u65bc\u5b57\u4e32\u6216\u5176\u4ed6\u985e\u578b\u7684\u8cc7\u6599\u7121\u6cd5\u8a08\u7b97\u5e73\u5747\u503c\u3002<\/li>\n<li>\u5982\u679c\u6240\u6709\u7684\u503c\u90fd\u662f NULL\uff0c\u5247 Avg \u51fd\u6578\u5c07\u8fd4\u56de NULL\u3002<\/li>\n<li>\u5728\u9032\u884c\u5206\u7d44\u67e5\u8a62\u6642\uff0cAvg \u51fd\u6578\u53ef\u4ee5\u8207 <code>GROUP BY<\/code> \u5b50\u53e5\u4e00\u8d77\u4f7f\u7528\uff0c\u4ee5\u8a08\u7b97\u6bcf\u500b\u7d44\u7684\u5e73\u5747\u503c\u3002<\/li>\n<\/ul>\n<h2 id=\"%e7%b5%90%e8%ab%96-poiGhWdFtf\">\u7d50\u8ad6<\/h2>\n<p>Avg \u51fd\u6578\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\uff0c\u4e26\u5728\u5404\u7a2e\u61c9\u7528\u5834\u666f\u4e2d\u767c\u63ee\u91cd\u8981\u4f5c\u7528\u3002\u7121\u8ad6\u662f\u5728\u696d\u52d9\u5206\u6790\u3001\u5b78\u8853\u7814\u7a76\u9084\u662f\u8ca1\u52d9\u6c7a\u7b56\u4e2d\uff0cAvg \u51fd\u6578\u90fd\u80fd\u63d0\u4f9b\u6709\u50f9\u503c\u7684\u898b\u89e3\u3002\u5c0d\u65bc\u9700\u8981\u9032\u884c\u6578\u64da\u5206\u6790\u7684\u7528\u6236\u4f86\u8aaa\uff0c\u638c\u63e1 Avg \u51fd\u6578\u7684\u4f7f\u7528\u65b9\u6cd5\u662f\u975e\u5e38\u91cd\u8981\u7684\u3002<\/p>\n<p>\u5982\u9700\u4e86\u89e3\u66f4\u591a\u6709\u95dc <a href=\"https:\/\/server.hk\">VPS<\/a> \u53ca\u5176\u4ed6\u76f8\u95dc\u670d\u52d9\u7684\u4fe1\u606f\uff0c\u8acb\u8a2a\u554f\u6211\u5011\u7684\u7db2\u7ad9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e86\u89e3 SQL \u805a\u5408\u51fd\u6578\u4e2d\u7684 Avg \u51fd\u6578\uff0c\u5b78\u7fd2\u5982\u4f55\u8a08\u7b97\u6578\u64da\u96c6\u7684\u5e73\u5747\u503c\uff0c\u63d0\u5347\u6578\u64da\u5206\u6790\u80fd\u529b\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-143853","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143853","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=143853"}],"version-history":[{"count":1,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143853\/revisions"}],"predecessor-version":[{"id":143854,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/143853\/revisions\/143854"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=143853"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=143853"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=143853"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}