That is because your query is generating a cartesian product.
Try:
SELECT ( SELECT SUM(totalprice) FROM invoices WHERE custnumber = '1'
) - ( SELECT SUM(paymentamount) FROM payments WHERE custnumber = '1'
)
Roy Souther wrote:
>
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> I have an invoice database that has two tables one for invoices and one for
> payments. I want to get the account balance for a client by subtracting the
> sum of all payments from the sum off all invoices for that client.
>
> Here is the SQL that I thought should work.
> SELECT SUM(t0.totalprice)-SUM(t1.paymentamount) FROM invoices t0, payments t1
> WHERE t0.custnumber='1' AND t1.custnumber='1'
>
> It works fine if there is only one invoice and one payment but as soon as
> there is more then one of either it screws up. For each match found in
> payments the invoice sum is added to the total. So if client 1 purchased a
> $100 item then maid a $10 payment the SQL would return the balance of $90
> just fine. When the client makes a second payment of $15 the balance is $75
> but this SQL returns ($100+$100)-($10+$15) = $175. A third payment of $1
> would return ($100+$100+$100)-($10+$15+$1) = $274.
>
> Could some one explain this to me and recommend an SQL command that would work
> please? I could do this using a temp table but that would be very messy as I
> would really like it to be a single SQL command.
> - --
> Roy Souther <roy@SiliconTao.com>
> http://www.SiliconTao.com
>
> Linux: May the source be with you.
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