From: Daniel CAUNE <d.caune@free.fr>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: Daniel Caune <daniel.caune@ubisoft.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Index on nullable column
Date: Sat, 25 Mar 2006 07:38:29 -0500
Message-ID: <0IWO00E7BOG2MP90@VL-MH-MR001.ip.videotron.ca> (raw)
In-Reply-To: <12727.1143244097@sss.pgh.pa.us>
> > Is an index on a nullable column useful for retrieving rows having that
> > column null?
>
> Nope, because IS NULL isn't an indexable operator.
>
> You can make an end-run around that with a partial index, eg
>
> create index fooi on foo(f1) where f1 is null
>
> This can be used to satisfy queries using "where f1 is null", but it's
> not any good for any other purpose.
>
> If you often do "where f1 is null and something-about-f2",
> you might get better mileage with
>
> create index fooi on foo(f2) where f1 is null
>
> but it's still a very specialized index.
>
Thanks Tom. I will use such an index even if it's very specialized; OLAP world is somewhat full of specialized index anyway... :-)
--
Daniel
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To: pgsql-sql@postgresql.org
Cc: d.caune@free.fr, tgl@sss.pgh.pa.us, daniel.caune@ubisoft.com
Subject: Re: Index on nullable column
In-Reply-To: <0IWO00E7BOG2MP90@VL-MH-MR001.ip.videotron.ca>
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