| From: | Richard Huxton <dev(at)archonet(dot)com> |
|---|---|
| To: | David Teran <david(dot)teran(at)cluster9(dot)com> |
| Cc: | PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: select max(id) from aTable is very slow |
| Date: | 2004-06-03 13:07:49 |
| Message-ID: | 40BF22A5.8060102@archonet.com |
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| Lists: | pgsql-performance |
David Teran wrote:
> Hi,
>
> we have a table with about 6.000.000 rows. There is an index on a
> column with the name id which is an integer and serves as primary key.
>
> When we execute select max(id) from theTable; it takes about 10
> seconds. Explain analyze returns:
Due to the open-ended nature of PG's aggregate function system, it can't
see inside the max() function to realise it doesn't need all the values.
Fortune favours the flexible however - the simple workaround is to use
the equivalent:
SELECT id FROM theTable ORDER BY id DESC LIMIT 1;
--
Richard Huxton
Archonet Ltd
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