Re: Major differences between oracle and postgres performance - what can I do ? - Mailing list pgsql-performance

=?iso-8859-1?q?Gary=20Cowell?= <gary_cowell@yahoo.co.uk> writes:
> So it seems the idea that oracle is dropping duplicate
> rows prior to the sort when using distinct may indeed
> be the case.

Okay.  We won't have any short-term solution for making DISTINCT do that,
but if you are on PG 7.4 you could get the same effect from using
GROUP BY: instead of
    select distinct version from vers where version is not null
try
    select version from vers where version is not null group by version
You should get a HashAggregate plan out of that, and I'd think it'd be
pretty quick when there are not many distinct values of version.

            regards, tom lane