SUM函数的SQL查询

Question

我有两张桌子贷款和会员。现在在贷款我有列totalamount和在成员我有列作为membertype和在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。

我尝试了以下内容：

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，那么就像这样：

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