Re: Bad SUM result

There're no another ways? It don't looks like optimal.

Petr Jezek
----- Original Message -----
From: "Jean-Luc Lachance" <jllachan@nsd.ca>
To: "Roy Souther" <roy@silicontao.com>
Cc: <pgsql-sql@postgresql.org>
Sent: Monday, July 08, 2002 5:22 PM
Subject: Re: [SQL] Bad SUM result


> 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:
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
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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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