From: Richard Huxton <dev@archonet.com>
To: Андрей Репко <repko@sart.must-ipra.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Index not used on group by
Date: Tue, 27 Sep 2005 11:48:15 +0100
Message-ID: <4339236F.7070403@archonet.com> (raw)
In-Reply-To: <144520928.20050927121431@sart.must-ipra.com>
References: <144520928.20050927121431@sart.must-ipra.com>
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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To: pgsql-performance@postgresql.org
Cc: dev@archonet.com, repko@sart.must-ipra.com
Subject: Re: Index not used on group by
In-Reply-To: <4339236F.7070403@archonet.com>
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