| From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
|---|---|
| To: | Kathy Zhu <Kathy(dot)Zhu(at)Sun(dot)COM> |
| Cc: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: group by |
| Date: | 2003-10-04 16:23:48 |
| Message-ID: | 20031004162348.GA31628@wolff.to |
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| Thread: | |
| Lists: | pgsql-general |
On Fri, Oct 03, 2003 at 17:32:22 -0600,
Kathy Zhu <Kathy(dot)Zhu(at)Sun(dot)COM> wrote:
> I did a vacuum and got the same result.
> I think the problem lies in there is swapping going for groupby when there is a
> large number of rows in the table, 5000 in this case.
>
> I guess I have to use group by with caution.
In 7.4 you will probably find the results more compatible.
For 7.3 and lower, the first case will use a sort to do a group by.
No sort will be done in the second example.
In 7.4 the groub by will use the new hash aggregate method and will
probably be significantly faster than the second way of doing things.
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