Re: distinct on doesn't fail without order by? why?

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