{"id":1706,"date":"2025-02-16T07:08:57","date_gmt":"2025-02-15T23:08:57","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=1706"},"modified":"2025-02-16T07:08:57","modified_gmt":"2025-02-15T23:08:57","slug":"sql-avg-%e5%87%bd%e6%95%b0","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/02\/16\/sql-avg-%e5%87%bd%e6%95%b0\/","title":{"rendered":"SQL\u00a0AVG()\u00a0\u51fd\u6570"},"content":{"rendered":"\n

\u5b66\u4e60 SQL \u51fd\u6570\u662f\u638c\u63e1 SQL \u5173\u952e\u90e8\u5206\u4e4b\u4e00\u3002 AVG()<\/code> \u51fd\u6570\u662f\u805a\u5408\u51fd\u6570\u4e4b\u4e00\uff0c\u7528\u4e8e\u8ba1\u7b97\u67d0\u4e2a\u5b57\u6bb5\u7684\u5e73\u5747\u503c\u3002\u63a5\u4e0b\u6765\u8ba9\u6211\u4eec\u4e00\u6b65\u4e00\u6b65\u5730\u6df1\u5165\u7406\u89e3\u8fd9\u4e2a\u51fd\u6570\uff0c\u5e76\u901a\u8fc7\u5b9e\u9645\u4f8b\u5b50\u6765\u8bf4\u660e\u5b83\u7684\u7528\u6cd5\u3002<\/p>\n\n\n\n

1. AVG()<\/code> \u51fd\u6570\u7b80\u4ecb<\/h3>\n\n\n\n

AVG()<\/code> \u51fd\u6570\u8fd4\u56de\u9009\u5b9a\u5217\u7684\u5e73\u5747\u503c\uff0c\u901a\u5e38\u7528\u4e8e\u6570\u5b57\u7c7b\u578b\u5b57\u6bb5\u3002\u5b83\u4f1a\u81ea\u52a8\u5ffd\u7565 NULL<\/code> \u503c\u3002<\/p>\n\n\n\n

2. \u57fa\u672c\u8bed\u6cd5<\/h3>\n\n\n\n
SELECT AVG(column_name)\nFROM table_name\nWHERE condition;<\/code><\/pre>\n\n\n\n
    \n
  • column_name<\/code>\uff1a\u4f60\u60f3\u8981\u8ba1\u7b97\u5e73\u5747\u503c\u7684\u5217\u3002<\/li>\n\n\n\n
  • table_name<\/code>\uff1a\u6570\u636e\u8868\u7684\u540d\u5b57\u3002<\/li>\n\n\n\n
  • condition<\/code>\uff1a\u53ef\u9009\uff0c\u7528\u4e8e\u8fc7\u6ee4\u6570\u636e\u7684\u6761\u4ef6\u3002<\/li>\n<\/ul>\n\n\n\n
    3. \u793a\u4f8b 1\uff1a\u8ba1\u7b97\u5de5\u8d44\u7684\u5e73\u5747\u503c<\/h3>\n\n\n\n
    \u5047\u8bbe\u4f60\u6709\u4e00\u4e2a\u5458\u5de5\u8868 employees<\/code>\uff0c\u5305\u542b\u4ee5\u4e0b\u5b57\u6bb5\uff1a<\/p>\n\n\n\n
    employee_id<\/th>name<\/th>salary<\/th><\/tr><\/thead>
    1<\/td>Tom<\/td>5000<\/td><\/tr>
    2<\/td>Jane<\/td>6000<\/td><\/tr>
    3<\/td>Bob<\/td>7000<\/td><\/tr>
    4<\/td>Alice<\/td>8000<\/td><\/tr>
    5<\/td>Mike<\/td>5500<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \u4f60\u53ef\u4ee5\u4f7f\u7528 AVG()<\/code> \u6765\u8ba1\u7b97\u6240\u6709\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44\uff1a<\/p>\n\n\n\n
    SELECT AVG(salary) AS avg_salary\nFROM employees;<\/code><\/pre>\n\n\n\n
    \u8f93\u51fa\uff1a<\/strong><\/p>\n\n\n\n
    avg_salary<\/th><\/tr><\/thead>
    6300<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    4. \u793a\u4f8b 2\uff1a\u8ba1\u7b97\u7279\u5b9a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44<\/h3>\n\n\n\n
    \u5047\u8bbe\u8868\u4e2d\u8fd8\u6709\u4e00\u4e2a department<\/code> \u5b57\u6bb5\uff0c\u8bb0\u5f55\u5458\u5de5\u6240\u5c5e\u7684\u90e8\u95e8\u3002\u4f60\u60f3\u8ba1\u7b97\u67d0\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\u3002\u4f8b\u5982\uff0c\u8ba1\u7b97 \u201cSales\u201d \u90e8\u95e8\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44\uff1a<\/p>\n\n\n\n
    SELECT AVG(salary) AS avg_salary\nFROM employees\nWHERE department = 'Sales';<\/code><\/pre>\n\n\n\n
    5. \u793a\u4f8b 3\uff1a\u4f7f\u7528 AVG()<\/code> \u7ed3\u5408 GROUP BY<\/code><\/h3>\n\n\n\n
    \u6709\u65f6\uff0c\u4f60\u53ef\u80fd\u9700\u8981\u6309\u67d0\u4e2a\u5206\u7c7b\u8fdb\u884c\u5206\u7ec4\u5e76\u8ba1\u7b97\u6bcf\u4e2a\u7ec4\u7684\u5e73\u5747\u503c\u3002\u6bd4\u5982\uff0c\u8ba1\u7b97\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\uff1a<\/p>\n\n\n\n
    SELECT department, AVG(salary) AS avg_salary\nFROM employees\nGROUP BY department;<\/code><\/pre>\n\n\n\n
    \u8f93\u51fa\uff1a<\/strong><\/p>\n\n\n\n
    department<\/th>avg_salary<\/th><\/tr><\/thead>
    Sales<\/td>6000<\/td><\/tr>
    HR<\/td>7000<\/td><\/tr>
    IT<\/td>7500<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    6. \u793a\u4f8b 4\uff1a\u6392\u9664 NULL<\/code> \u503c<\/h3>\n\n\n\n
    AVG()<\/code> \u51fd\u6570\u4f1a\u81ea\u52a8\u5ffd\u7565 NULL<\/code> \u503c\u3002\u5982\u679c\u67d0\u4e9b\u5458\u5de5\u7684\u5de5\u8d44\u5b57\u6bb5\u662f NULL<\/code>\uff0c\u5b83\u4eec\u4e0d\u4f1a\u5f71\u54cd\u7ed3\u679c\u3002\u5047\u8bbe\u5458\u5de5\u8868\u4e2d\u6709\u4e9b salary<\/code> \u4e3a NULL<\/code>\uff1a<\/p>\n\n\n\n
    SELECT AVG(salary) AS avg_salary\nFROM employees\nWHERE salary IS NOT NULL;<\/code><\/pre>\n\n\n\n
    \u8fd9\u5c06\u8ba1\u7b97\u6240\u6709\u975e NULL<\/code> \u5de5\u8d44\u7684\u5e73\u5747\u503c\u3002<\/p>\n\n\n\n
    7. \u8fdb\u9636\u7528\u6cd5<\/h3>\n\n\n\n
    \u4f60\u8fd8\u53ef\u4ee5\u5c06 AVG()<\/code> \u51fd\u6570\u4e0e\u5176\u4ed6\u51fd\u6570\u7ed3\u5408\u4f7f\u7528\uff0c\u4f8b\u5982\u4f7f\u7528 CASE<\/code> \u6765\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\uff1a<\/p>\n\n\n\n
    SELECT \n  department,\n  AVG(CASE WHEN salary > 6000 THEN salary END) AS avg_high_salary\nFROM employees\nGROUP BY department;<\/code><\/pre>\n\n\n\n
    \u8fd9\u4e2a\u4f8b\u5b50\u8ba1\u7b97\u4e86\u6bcf\u4e2a\u90e8\u95e8\u5de5\u8d44\u5927\u4e8e 6000 \u7684\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44\u3002<\/p>\n\n\n\n
    \n\n\n\n
    \u8fd9\u4e9b\u793a\u4f8b\u5c55\u793a\u4e86 AVG()<\/code> \u51fd\u6570\u7684\u57fa\u672c\u548c\u8fdb\u9636\u7528\u6cd5\uff0c\u53ef\u4ee5\u5e94\u7528\u4e8e\u591a\u79cd\u5b9e\u9645\u573a\u666f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u5b66\u4e60 SQL \u51fd\u6570\u662f\u638c\u63e1 SQL \u5173\u952e\u90e8\u5206\u4e4b\u4e00\u3002 AVG() \u51fd\u6570\u662f\u805a\u5408\u51fd\u6570\u4e4b\u4e00\uff0c\u7528\u4e8e\u8ba1\u7b97\u67d0\u4e2a\u5b57\u6bb5\u7684\u5e73\u5747\u503c\u3002\u63a5 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[36],"tags":[],"class_list":["post-1706","post","type-post","status-publish","format-standard","hentry","category-sql"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/1706","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=1706"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/1706\/revisions"}],"predecessor-version":[{"id":1707,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/1706\/revisions\/1707"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=1706"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=1706"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=1706"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}