| From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Sean Shanny <shannyconsulting(at)earthlink(dot)net>, "Pgsql-General(at)Postgresql(dot)Org (E-mail)" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Query performance question on a large table |
| Date: | 2004-01-07 17:43:07 |
| Message-ID: | 20040107174307.GC12631@wolff.to |
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| Lists: | pgsql-general |
On Wed, Jan 07, 2004 at 02:31:22 -0500,
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> I just a couple days ago added some logic to CVS tip to notice that the
> sub-select has a DISTINCT clause, and not add unnecessary unique-ifying
> processing on top of it. So in 7.5, writing a DISTINCT clause will
> amount to forcing a particular query plan, which might or might not be
> the best thing but hopefully won't be too terrible. But in 7.4 it has
> nothing to recommend it ...
Can't the DISTINCT be dropped if there isn't a LIMIT clause?
Similarly UNION, INTERSECTION and EXCEPT could also also be changed
to the ALL forms if there isn't a LIMIT.
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