2010/10/15 Tom Lane <tgl@sss.pgh.pa.us>:
> Hitoshi Harada <umi.tanuki@gmail.com> writes:
>> UNION DISTINCT is nothing more than UNION itself, but gram.y
>> definitely accept it and the SQL standard describes it as well. Should
>> we add DISTINCT to docs?
>
> I think it'd be hard to describe without confusing people, because
> while DISTINCT is a noise word there, it's definitely not a noise
> word after SELECT. And the way that the reference pages are laid
> out, it's hard to connect different descriptions of the same
> keyword to different usages. If you can think of a non-forced
> way of describing this, fine. But I don't have a problem with
> leaving it as an undocumented standards-compliance nit.
I thought adding DISTINCT next to ALL is enough like
select_statement UNION [ ALL | DISTINCT ] select_statement
and say "UNION DISTINCT is identical to UNION only" or something. That
sounds not so confusing with DISTINCT clause description.
Regards,
--
Hitoshi Harada