Re: DISTINCT vs. GROUP BY

On Tue, Sep 20, 2005 at 05:05:05PM -0400, Bruce Momjian wrote:
> Jim C. Nasby wrote:
> > On Mon, Sep 19, 2005 at 10:16:36PM -0400, Bruce Momjian wrote:
> > >
> > > Added to TODO:
> > >
> > > * Allow DISTINCT to use hashing like GROUP BY
> >
> > 3 lines above we have...
> > Consider using hash buckets to do DISTINCT, rather than sorting
> > This would be beneficial when there are few distinct values.
>
> OK, I have merged these items into one.
>
> >
> > Can you add
> > http://archives.postgresql.org/pgsql-hackers/2005-09/msg00810.php? All I
> > could find on the other TODO was
> > http://archives.postgresql.org/pgsql-committers/2004-09/msg00028.php,
> > which doesn't help much...
>
> What do these URL's have that the current TODO does not?
>
> * Consider using hash buckets to do DISTINCT, rather than sorting
>
> This would be beneficial when there are few distinct values. This is
> already used by GROUP BY.

Maybe it's just me, but the recent run-through of the TODO list
indicated that there's a fair number of items that people look at and
don't really knowh what they mean. Providing the context (ie: email
thread) that spawned an idea seems extremely valuable in being able to
explain the idea behind a TODO item. They also usually contain valuable
tips about how a TODO could be implemented. In this example, having
quick reference to the discussion about hashagg and first()/last() would
probably prove useful.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461