Re: procedures and plpgsql PERFORM

On Thu, Dec 14, 2017 at 8:22 AM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:

> On Thu, Dec 14, 2017 at 8:38 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> writes:
> >> We allow a function to be invoked as part of PERFORM statement in
> plpgsql
> >> ...
> >> But we do not allow a procedure to be invoked this way
> >
> >> Procedures fit that category and like functions, I think, we should
> >> allow them be invoked directly without any quoting and CALL
> >> decoration.
> >
> > How is that going to work? What if the procedure tries to commit the
> > current transaction?
> >
> > IOW, this is not merely a syntactic-sugar question.
>
> BTW, We've already come to (near-but good enough) consensus that
> PERFORM syntax is really just unnecessary, and I submitted a patch to
> make it optional (which I really need to dust off and complete).

​Except right now PERFORM doesn't exist in SQL and is a pl/pgsql keyword to
specify a specific limited form of the SQL SELECT command. CALL is an SQL
command. I don't see any real upside to allowing pl/pgsql to accept
omission of the command tag while SQL cannot - at least not without a
use-case describe why such syntax would be beneficial. And likely those
use cases would revolve around some looping variant as opposed to a single
stand-alone, result-less, CALL.

If we do keep "PERFORM" in the pl/pgsql vocab I'd consider the following
enhancement:
PERFORM func() => SELECT func()
PERFORM proc() => CALL proc()

I prefer Merlin's suggestion to just documenting that PERFORM is deprecated
and works only with functions - and that to use procedures in pl/pgsql just
use the normal SQL CALL command. And to write: "SELECT func()" to invoke
functions, again just like one would in an SQL script.

David J.