無效使用GROUP BY的運營商WHERE子句

Question

下面的查詢成功返回誰已打印的最具體的用戶（通過ID）後：

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) 

當我介紹where子句來儘量消除用戶誰在所有未打印（也就是，其中sum（print_pages）== 0），我寫了下面的查詢：

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) 

，並出現以下錯誤：

#1111 - Invalid use of group function 

如何消除sum（print_pages）有0的結果？

Answer 1

這是因爲你不能使用聚合函數WHERE條款。因此，使用HAVING這樣的子句：

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

您需要使用具有關鍵字，而不是因爲你是工作的一個總：

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)