How to group by two field? : I have the following table:

    listId | accountId | ammount | 
    1        1           20
    1        1           20
    2        2           30
    2        2           30

I need to `sum(ammount)` and group by `listId, accountId` to get result:

     listId | accountId | ammount | 
     1        1           40
     2        2           60

But this does not work for me: `SUM(ammount) ... GROUP BY listId, accountId`

