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@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461