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Date: Fri, 8 Jul 2005 09:07:25 -0500
From: Bruno Wolff III <bruno@wolff.to>
To: PFC <lists@boutiquenumerique.com>
Cc: Kenneth Gonsalves <lawgon@thenilgiris.com>,
	Ramakrishnan Muralidharan <ramakrishnanm@pervasive-postgres.com>,
	pgsql-sql@postgresql.org
Subject: Re: two sums in one query
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On Fri, Jul 08, 2005 at 15:49:20 +0200,
  PFC <lists@boutiquenumerique.com> wrote:
> 
> 
> >>   SELECT  SUM( CASE WHEN COALESCE( DEBIT , 0 ) <> 0 THEN
> >>COALESCE( AMOUNT , 0 ) ELSE 0 END ) AS DEBIT_AMT , SUM( CASE WHEN
> >>COALESCE( CREDIT , 0 ) <> 0 THEN   COALESCE( AMOUNT , 0 ) ELSE 0
> >>END ) AS CREDIT_AMT FROM <TABLE NAME>
> 
> 	I don't know if it will use indexes (bitmapped OR indexes in 8.1 
> 	?)... if  you have indexes on debit and on credit, you could do
> 
> SELECT (SELECT sum(amount) FROM table WHERE debit=X) AS debit, (SELECT  
> sum(amount) FROM table WHERE credit=x) AS credit;

If most of the records are credits or debits you don't want to do this.
A single sequential scan through the table will be the best plan.