From: | Tomasz Rybak <bogomips(at)post(dot)pl> |
---|---|
To: | "Craig A(dot) James" <cjames(at)modgraph-usa(dot)com> |
Cc: | Kishore B <kishorebh(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Need help in setting optimal configuration for a huge |
Date: | 2005-10-23 17:17:56 |
Message-ID: | 1130087877.6708.16.camel@localhost.localdomain |
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Lists: | pgsql-admin pgsql-performance |
Dnia 23-10-2005, nie o godzinie 09:31 -0700, Craig A. James napisał(a):
<cut>
> MIN() and MAX() -- These are surprisingly slow, because they seem to do a full table scan EVEN ON AN INDEXED COLUMN!
In 8.1 this is no true, see the changelog.
> I don't understand why, but happily there is an effective substitute:
>
> select mycolumn from mytable order by mycolumn limit 1; -- same as MIN()
>
> select mycolumn from mytable order by mycolumn desc limit 1; -- same as MAX()
In 8.1 these queries are equivalent:
select mycolumn from mytable order by mycolumn limit 1;
select min(mycolumn) from mytable;
--
Tomasz Rybak <bogomips(at)post(dot)pl>
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