如何从MySQL的视图中选择一个字段？

Question

如何在MySQL中做以下查询？

Select SUM(T1.Amount) 
From 
( 
    Select Distinct PersonName,Amount 
    From tblusers as T1 
    where city ="xxx" 
) 

Answer 1

MySQL需要派生表或子查询上的别名。所以，你会希望使用以下命令：

Select SUM(t1.Amount) 
From 
( 
    Select Distinct PersonName, Amount 
    From tblusers 
    where city ="xxx" 
) t1 

您应该能够使用以下虽然根据您的需要：

select personName, sum(Amount) 
from tblusers 
where city = "xxx" 
group by personName 

或者，如果你只是想返回的总和，你可以使用：

select sum(Amount) 
from tblusers 
where city = "xxx" 
group by personName 

Answer 2

只是别名的子查询：

Select SUM(Amount) 
From (
    Select Distinct PersonName, Amount 
    From tblusers 
    where city ="xxx") t 

如果你正在寻找每个人，增加一个GROUP BY：

Select PersonName, SUM(Amount) 
From (
    Select Distinct PersonName, Amount 
    From tblusers 
    where city ="xxx") t 
Group By PersonName 

如果你真的想每个人的总和（而不是不同人物/金额的总和），那么你完全不需要子查询：

Select PersonName, SUM(Amount) 
From tblusers 
Where city ="xxx" 
Group By PersonName 

虽然取决于您的实际需求。

Answer 3

我做了下面的查询。但想知道是否有任何其他可能的方式来做到这一点。

CREATE VIEW T1 as (Select Distinct PersonName,Amount From tblusers where city ="xxx"); 

    Select SUM(Amount) From T1