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Re: EXISTS vs IN vs OUTER JOINS

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Joe Conway <mail(at)joeconway(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>,Tomasz Myrta <jasiek(at)klaster(dot)net>,PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org>
Subject: Re: EXISTS vs IN vs OUTER JOINS
Date: 2002-12-19 22:52:24
Message-ID: 200212192252.gBJMqON27748@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane wrote:
> Joe Conway <mail(at)joeconway(dot)com> writes:
> > I wonder if "[NOT] IN (subselect)" could be improved with a hash table in 
> > similar fashion to the hash aggregate solution Tom recently implemented?
> 
> It's being worked on ;-)
> 
> http://archives.postgresql.org/pgsql-hackers/2002-11/msg01055.php
> 
> Assuming I get this done, the conventional wisdom that "EXISTS
> outperforms IN" will be stood on its head --- unless we add planner code
> to try to reverse-engineer an IN from an EXISTS, which is something I'm
> not really eager to expend code and cycles on.

I am looking forward to removing _that_ FAQ item.  :-)

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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