Re: DISTINCT vs. GROUP BY

On Mon, 2005-19-09 at 16:27 +0200, Hans-Jürgen Schönig wrote:
> I was wondering whether it is possible to teach the planner to handle 
> DISTINCT in a more efficient way:
[...]
> Isn't it possible to perform the same operation using a
> HashAggregate? 

One problem is that DISTINCT ON is defined to return the first unique
row (according to the query's ORDER BY) for the set of DISTINCT ON
columns, which can't easily be done via hashing.

-Neil