Question

Hey guys, I have a program that allows me to run queries against a large database.
I have two tables that are important right now, Deposits and withdraws. Each contains a history of every user. I need to take each table, add up every deposit and withdraws (per user), then subtract the withdraws from the deposits. I then need to return every user whos result is negative (aka they withdrew more then they deposited).
Is this possible in one query?
Example:

Deposit Table:

|ID|UserName|Amount|
|1 |  Use1  |100.00|
|2 |  Use1  |50.00 |
|3 |  Use2  |25.00 |
|4 |  Use1  | 5.00 |


WithDraw Table:
|ID|UserName|Amount|
|2 |  Use2  | 5.00 |
|1 |  Use1  |100.00|
|4 |  Use1  | 5.00 |
|3 |  Use2  |25.00 |

So then the result would output:
|OverWithdrawers|
|      Use2     |

Is this possible (I sure don’t know how to do it)?
Thanks for any help,
Max

Answer 1

Try this:

SELECT T1.UserName
FROM
(
    SELECT UserName, SUM(Amount) AS Amount
    FROM WithDraw
    GROUP BY UserName
) T1
LEFT JOIN
(
    SELECT UserName, SUM(Amount) AS Amount
    FROM Deposit
    GROUP BY UserName
) T2
ON T1.UserName = T2.UserName
WHERE T1.Amount > COALESCE(T2.Amount, 0)

The COALESCE is so that it also works if there are users that have withdrawn but never deposited.