Mailbox-Line: From jllachan@nsd.ca  Mon Jul  8 14:01:25 2002
Message-ID: <3D29AE37.ADE9D534@nsd.ca>
Date: Mon, 08 Jul 2002 11:22:31 -0400
From: Jean-Luc Lachance <jllachan@nsd.ca>
MIME-Version: 1.0
To: Roy Souther <roy@silicontao.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Bad SUM result
References: <200207071425.56235.roy@silicontao.com>
Content-Type: text/plain; charset=us-ascii
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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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