From: Ken Geis <kgeis@speakeasy.org>
To: Bruno Wolff III <bruno@wolff.to>
Cc: pgsql-performance@postgresql.org
Subject: Re: bad estimates / non-scanning aggregates
Date: Thu, 28 Aug 2003 19:50:38 -0700
Message-ID: <3F4EBF7E.8020602@speakeasy.org> (raw)
In-Reply-To: <20030829025109.GD4373@wolff.to>
References: <3F4E99F7.7080604@speakeasy.org>
<20030829025109.GD4373@wolff.to>
Bruno Wolff III wrote:
> On Thu, Aug 28, 2003 at 17:10:31 -0700,
> Ken Geis <kgeis@speakeasy.org> wrote:
>
>>The query I want to run is
>>
>>select stock_id, min(price_date) from day_ends group by stock_id;
>
> The fast way to do this is:
>
> select distinct on (stock_id) stock_id, price_date
> order by stock_id, price_date;
Not according to the optimizer! Plus, this is not guaranteed to return
the correct results.
Unique (cost=3711244.30..3795942.42 rows=6366 width=8)
-> Sort (cost=3711244.30..3753593.36 rows=16939624 width=8)
Sort Key: stock_id, price_date
-> Seq Scan on day_ends (cost=0.00..361892.24 rows=16939624
width=8)
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To: pgsql-performance@postgresql.org
Cc: kgeis@speakeasy.org, bruno@wolff.to
Subject: Re: bad estimates / non-scanning aggregates
In-Reply-To: <3F4EBF7E.8020602@speakeasy.org>
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