How to select from one table where difference with (sum) from another table?

Question

I have two tables with following fields:
...

orders.orderID
orders.orderValue

and

payments.orderID
payments.payVal

In payments.payVal there will be incremental payments for each order (many-to-one).
What I need it so select ALL orders from orders where there is payment left (orders.orderValue - ((sum)payments.payVal) > 0 ) .

The only thing I can come up to right now is a (foreach) using the orderID , but I cannot do that for some particular reasons. I also cannot add a column inside table to hold the value for some reasons too.

What I need, is to perform the entire selection in one single SQL Query something that resembles this idea: SELECT * FROM orders WHERE <... each(orderValue - (sum(payVal))) > 0 ...>

Answer 1

SELECT *, SUM(p.payVal) AS TotalPayed
FROM orders o
LEFT JOIN payments p ON o.orderID = p.orderID
GROUP BY o.orderID
HAVING SUM(p.payVal) < o.orderValue

This should provide you with the necessary fields, although I would advise you to select specific fields with this query.

The LEFT JOIN makes sure you get every order, even if there are no payments made yet.

SQL Fiddle

Answer 2

Looks like we came to the same solution,

http://sqlfiddle.com/#!2/9a657/18

SELECT * FROM `orders`
LEFT JOIN `payments` AS p ON `orders`.`orderID` = p.`orderID`
GROUP BY `orders`.`orderID`
HAVING SUM(p.`payVal`) <= 0