SQL查询SUM函数

Question

我有两个表Loan和Member。现在在贷款我有列totalamount和成员我有专栏作为membertype和贷款我有各种贷款根据membertype。现在我想使用SUM函数根据memtype计算totalamount。

我试过的东西如下：

select sum(totalamount) from loan,member where member.mem_type='Regular' 

Answer 1

你的意思是这样的：

select sum(totalamount) AS Total 
from loan 
JOIN member ON Memberid=loan.Memberid 
where member.mem_type='Regular' 

或者，如果你想选择mem_type还有那么这样的事情：

select sum(totalamount) AS Total,member.mem_type 
from loan 
JOIN member ON Memberid=loan.Memberid 
where member.mem_type='Regular' 
GROUP BY member.mem_type