Question

Help please, I have a table like this:

 | ID | userId   | amount  | type    |
 -------------------------------------
 |  1 |       10 |  10     | expense |
 |  2 |       10 |  22     | income  |
 |  3 |        3 |  25     | expense |
 |  4 |        3 |  40     | expense |
 |  5 |        3 |  63     | income  |

I’m looking for a way to use one query and retrive the balance of each user.

The hard part comes when the amounts has to be added on expenses and substracted on incomes.

This would be the result table:

 | userId | balance |
 --------------------
 |   10   |  12     |
 |    3   |  -2     |

Answer 1

This is easiest to do with a single group by:

select user_id,
       sum(case when type = 'income' then amount else - amount end) as balance
from t
group by user_id