Sum函数可以连接三个表

Question

我有三张桌子如下所述

Main_id | Main _name
--------+-----------
1       | A
2       | B

Sub_id | Sub_name  | Main_id   (foreign key from main table) 
-------+-----------+--------
11     | AA        | 1 
12     | AB        | 1
22     | BB        | 2

Transaction_ID  | Amount  | Sub_id  (foreign key from sub table)  
----------------+---------+---------
1               | 100     |  11
1               | 200     |  11
1               |  50     |  22

我希望每个主要帐户都有交易总额，所以它看起来像 每个主要ID及其总金额

的SQL查询是什么？

Main_id | Total Amount
--------+---------------
1       | 300
2       |  50 

什么是SQL查询？

Answer 1

select Main_id, sum(Amount) "Total Amount"
from Table1 inner join Table2 using(Main_id)
            inner join Table3 using(Sub_id)
group by Main_id
order by 1;

  

MAIN_ID总金额

     

     1          300
     2           50