Re: [HACKERS] DISTINCT ON: speak now or forever hold your peace

Tom Lane wrote:
>
> If I don't hear loud hollers very soon, I'm going to eliminate the
> DISTINCT ON "feature" for 7.0. As previously discussed, this feature
> is not standard SQL and has no clear semantic interpretation.

I don't feel overly strongly about this, but if I remember right you can
do some pretty cool things with this feature, provided you do define
some semantics clearly. Like I think you can find the first tuple
(given some ORDER BY clause) that fulfills some criteria. I think it is

SELECT DISTINCT ON name name, age ORDER BY age;

will get the youngest person. This might not be clearly specified now,
but
as long as it's useful, how about clearly defining it? I don't know that
there is an easy way of doing this in standard SQL. I don't see any
problems with useful extensions to SQL. If people want standards, they
don't have to use it.