SQL查詢SUM函數

Question

我有兩個表Loan和Member。現在在貸款我有列totalamount和成員我有專欄作爲membertype和貸款我有各種貸款根據membertype。現在我想使用SUM函數根據memtype計算totalamount。

我試過的東西如下：

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

Answer 1

你的意思是這樣的：

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

或者，如果你想選擇mem_type還有那麼這樣的事情：

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