From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Greg Stark <gsstark(at)mit(dot)edu> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Optimizer picks an ineffient plan |
Date: | 2003-09-04 02:44:25 |
Message-ID: | 4375.1062643465@sss.pgh.pa.us |
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Lists: | pgsql-general |
Greg Stark <gsstark(at)mit(dot)edu> writes:
> "Bupp Phillips" <hello(at)noname(dot)com> writes:
>> select * from customer order by customer_id, first_name;
>> [ where customer_id is the primary key ]
> However you do have a point. In this case I don't think postgres even
> considers using the index.
It will not, since the index does not appear to provide the correct sort
order.
> However I'm not sure I see a lot of cases where this would come up.
Yes, that's the real crux of the matter. Should the optimizer spend
cycles on *every* query to detect cases where the user has written
useless sort keys? I've got grave doubts that it's a win. ISTM such
an optimization penalizes the folk who write their queries well to
benefit those who are careless.
regards, tom lane
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