Thread: Bad SUM result

Bad SUM result

From
Roy Souther
Date:
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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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Re: Bad SUM result

From
Stephan Szabo
Date:
On Sun, 7 Jul 2002, Roy Souther wrote:

> 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.

Right, because you're doing a join that ends up with
100 | 10
100 | 15
100 | 1

as the effective rows.


> 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.

Maybe something like:
select sum(amt) from (select custnumber, totalprice as amt from
invoices union select custnumber, -paymentamount as amt from payments) as
c where custnumber='1';





Re: Bad SUM result

From
Jean-Luc Lachance
Date:
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-----
> Hash: SHA1
> 
> 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.
> 
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.0.6 (GNU/Linux)
> Comment: For info see http://www.gnupg.org
> 
> iEYEARECAAYFAj0oo9MACgkQCbnxcmEBt43qFQCgtjCs7khKGH+2LYd78O9mA3h4
> vDQAn0GkKkuYl1Kybgm/ITO4LbO1WWLX
> =1G4R
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Re: Bad SUM result

From
Petr Jezek
Date:
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-----
> > Hash: SHA1
> >
> > 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.
> >
> > -----BEGIN PGP SIGNATURE-----
> > Version: GnuPG v1.0.6 (GNU/Linux)
> > Comment: For info see http://www.gnupg.org
> >
> > iEYEARECAAYFAj0oo9MACgkQCbnxcmEBt43qFQCgtjCs7khKGH+2LYd78O9mA3h4
> > vDQAn0GkKkuYl1Kybgm/ITO4LbO1WWLX
> > =1G4R
> > -----END PGP SIGNATURE-----
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
>
>
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