On 7/13/06,
Richard Broersma Jr <
rabroersma@yahoo.com> wrote:
> > SELECT controller_id FROM control
> > WHERE controller_id NOT IN
> > (SELECT DISTINCT controller_id FROM datapack);
> The DISTINCT is not necessary. I have heard with Oracle that DISTINCT is a
> huge performance problem. Is that true on PostgreSQL also?
From my experience, it does not preform as well as the standard group by clause. I noticed a ~20%
increase in query run times.
So in that case this would be better:
SELECT controller_id FROM control
WHERE controller_id NOT IN
(SELECT controller_id FROM datapack);
or
SELECT controller_id FROM control
WHERE controller_id NOT IN
(SELECT controller_id FROM datapack GROUP BY controller_id);Guess you need to do some explain plans to see which would be best.
Good luck!
==================================================================
Aaron Bono
Aranya Software Technologies, Inc.
http://www.aranya.com==================================================================