WHERE子句后无效使用GROUP BY运算符

Question

以下查询成功返回打印最多的特定用户（按ID）：

SELECT file_prints.user_id, user.major, sum(print_pages) FROM `file_prints`
INNER JOIN `user` on file_prints.user_id = user.user_id GROUP BY
file_prints.user_id 
ORDER BY sum(print_pages)

当我引入where子句以消除根本不打印的用户时（即where sum（print_pages）== 0），我编写以下查询：

SELECT file_prints.user_id, user.major, sum(print_pages) FROM `file_prints`
INNER JOIN `user` on file_prints.user_id = user.user_id WHERE
sum(print_pages) > 0 GROUP BY file_prints.user_id 
ORDER BY sum(print_pages)

并得到以下错误：

 #1111 - Invalid use of group function 

如何消除总和（print_pages）为0的结果？

Answer 1

这是因为您不能在WHERE子句中使用聚合函数。 因此，像这样使用HAVING子句：

SELECT file_prints.user_id, user.major, sum(print_pages) 
FROM `file_prints`
INNER JOIN `user` on file_prints.user_id = user.user_id
GROUP BY file_prints.user_id
HAVING sum(print_pages) > 0 
ORDER BY sum(print_pages)

Answer 2

在处理聚合时，您需要改用hading关键字：

SELECT file_prints.user_id, user.major, sum(print_pages) FROM `file_prints`
INNER JOIN `user` on file_prints.user_id = user.user_id 
GROUP BY file_prints.user_id 
HAVING sum(print_pages) > 0 
ORDER BY sum(print_pages)