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Re: Index not used on group by

From: Richard Huxton <dev(at)archonet(dot)com>
To: Андрей Репко <repko(at)sart(dot)must-ipra(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Index not used on group by
Date: 2005-09-27 10:48:15
Message-ID: 4339236F.7070403@archonet.com (view raw or flat)
Thread:
Lists: pgsql-performance
Andrey Repko wrote:
> 
>     I have table ma_data, that contain above 300000 rows.
>    This table has primary key id, and field alias_id.
>    I create index (btree)on this field.
>    Set statistic:
> 
>  ALTER TABLE "public"."ma_data"
>    ALTER COLUMN "alias_id" SET STATISTICS 998;
> 
>    So, when I do something like
>      SELECT alias_id FROM ma_data GROUP BY alias_id

Why are you using GROUP BY without any aggregate functions?

What happens if you use something like
   SELECT DISTINCT alias_id FROM ma_data;

--
   Richard Huxton
   Archonet Ltd

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