MySQL與MAX的分組不能按預期工作？

Question

我有一張桌子：

ID | User | Amount
1  | 1    | 50
2  | 1    | 80
3  | 2    | 80
4  | 2    | 100
5  | 1    | 90
6  | 1    | 120
7  | 2    | 120
8  | 1    | 150
9  | 2    | 300

我查詢：

SELECT * FROM TABLE ORDER BY amount DESC group by userid

我得到這個：

ID | User | Amount
1  | 1    | 50
2  | 1    | 80

但是我期待着：

ID | User | Amount
9  | 2    | 300
8  | 1    | 150

我的SQL有什么問題？

Answer 1

分組時，必須對所有未按分組的列使用諸如max()類的聚合函數

select t.* 
from table t
inner join 
(
   SELECT userid, max(amount) as total
   FROM TABLE 
   group by userid
) x on x.userid = t.userid and x.total = t.amount
ORDER BY t.amount DESC 

Answer 2

另一種解決方案。使用FIND_IN_SET子句檢查SQL Fiddle

SELECT
  ua.*
FROM user_amount ua
WHERE FIND_IN_SET(ua.amount,(SELECT
                               MAX(ua1.amount)
                             FROM user_amount ua1
                             WHERE ua1.user = ua.user)) > 0
ORDER BY amount desc;  

使用IN子句

SELECT
  ua.*
FROM user_amount ua
WHERE ua.amount IN (SELECT
                               MAX(ua1.amount)
                             FROM user_amount ua1
                             WHERE ua1.user = ua.user)
ORDER BY amount desc