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Date: Thu, 14 May 1998 18:10:02 +0300
From: Hannu Krosing <hannu@trust.ee>
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To: Olaf Mittelstaedt <mstaedt@va-sigi.va.fh-ulm.de>
CC: pgsql-interfaces@postgreSQL.org
Subject: Re: [INTERFACES] Re: Index unused with OR?
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Olaf Mittelstaedt wrote:

This is probably the wrong list, but ...
 
> Actually, I discovered the problem using a table containg more than
> 8000 rows, using the latest release 6.3.2.
> 
> > Not using the index in OR queries was some-time ago a bug in
> > PostgreSQL 6.1 if my memory is good. Think that has been solved in
> > new releases, am I wrong ?

seems _not_ to be fixed :(
 
> VACUUM
> w=> explain select * from p where m = 29000;
> NOTICE:  QUERY PLAN:
> 
> Index Scan on p  (cost=0.00 size=0 width=10)
> 
> EXPLAIN
> w=> explain select * from p where (m=29000) or (m=30000);
> NOTICE: QUERY PLAN:
> 
> Seq Scan on p (cost=0.00 size=0 width=10)
> 

As a work-around try

select * from p where (m=29000) union select * from p where (m=30000);

it should be much faster.

Btw, EXPLAIN thinks this to cost nothing ;)

Unique  (cost=0.00 size=0 width=0)
  ->  Sort  (cost=0.00 size=0 width=0)
        ->  Append  (cost=0.00 size=0 width=0)


Hannu