| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | depesz(at)depesz(dot)com |
| Cc: | pgsql-bugs(at)postgresql(dot)org |
| Subject: | Re: distinct on doesn't fail without order by? why? |
| Date: | 2009-05-18 21:56:33 |
| Message-ID: | 1242683793.26009.29.camel@monkey-cat.sm.truviso.com |
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| Lists: | pgsql-bugs |
On Mon, 2009-05-18 at 20:24 +0200, hubert depesz lubaczewski wrote:
> I was under impression that select distinct on (xx) ...
> will fail if xx doesn't match the left most part of order by. i.e. it
> requires order by xx, while allowing order by xx, something, else.
>
> But it seems you can run the query with no order by clause at all.
>
> is it intentional?
This is documented behavior:
"Note that the 'first row' of each set is unpredictable unless ORDER BY
is used to ensure that the desired row appears first."
http://www.postgresql.org/docs/8.4/static/sql-select.html#SQL-DISTINCT
Regards,
Jeff Davis
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