Using multiple JOINS. SUM() producing wrong value

Question

I am getting some basic invoice information in a SQL query and figuring the Order Total and Payment Totals in the same query. Here is what I have thus far:

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Answer 1

my guess is that the payment is $10 and there are two items in the order (orderitems table). if that's the case, try using a GROUP BY on the orders/customers/orderstatus fields.

Answer 2

If you run the query without a group by, you'll see that some payments have multiple rows. That's because you're also joining on order items. The result set will contain a row for each combination of orderitem and payment.

One solution would be to change the sum to:

,    <earlier columns>    
,    (   select SUM(payments.amount) 
         from payments 
         where payments.orderID = orders.id
     ) AS totalPayments
,    <later columns>

This would ensure the payments with multiple orderitems are not summed multiple times.