Vik Fearing <vik.fearing@2ndquadrant.com> writes:
> On 29/10/2019 12:24, Isaac Morland wrote:
>> If you need to refer specifically to the non-qualified version in a
>> different part of the query, you can give an alias to the result of
>> the join:
>> ... (a join b using (z)) as t ...
> Yes, this is about having standard SQL syntax for that.
Please present an argument why this proposal is standard SQL syntax.
I see no support for it in the spec. AFAICS this proposal is just an
inconsistent wart; it makes it possible to write
(a join b using (z) as q) as t
and then what do you do? Moreover, why should you be able to
attach an alias to a USING join but not other sorts of joins?
After digging around in the spec for awhile, it seems like
there actually isn't any way to attach an alias to a join
per spec.
According to SQL:2011 7.6 <table reference>, you can attach an
AS clause to every variant of <table primary> *except* the
<parenthesized joined table> variant. And there's nothing
about AS clauses in 7.7 <joined table>, which is where it would
have to be mentioned if this proposal were spec-compliant.
What our grammar effectively does is to allow an AS clause to be
attached to <parenthesized joined table> as well, which seems
like the most natural thing to do if the committee ever decide
to rectify the shortcoming.
Anyway, we already have the functionality covered, and I don't
think we need another non-spec, non-orthogonal way to do it.
regards, tom lane