连接两个表以按结果分组，包括两个表的列

Question

I have two different tables but one tables has primary key of another one. I am doing group by on one table, but need a particular column in result of another table.

Table1 Transaction { Column transaction_id, Column currency } Table2 Payment { Column payment_id, Column transaction_id, Column user_id, Column pay }

I want to get result in such a way that it is grouped by user_id and currency. Result has sum of pay for different user_id, currency combination.

For example

Transaction
transaction_id   currency
1                Dollar
2                Yun
3                Dollar

Payment
payment_id  transaction_id user_id pay
1           1              1       30
2           1              2       20
3           2              1       10
4           3              1       30

Result should have:

User_id 1
Currency Dollar
Pay 30

user_id 1
Currency Yun
Pay 10

user_id 2
Currency Dollar
Pay 20

Answer 1

This is a very simple Join

Select  P.User_Id, T.Currency, Sum(P.Pay)
From    Payment         P
Join    Transaction     T On T.Transaction_Id = P.Transaction_Id
Group By P.User_Id, T.Currency