Re: Using scalar function as set-returning: bug or feature?

Moin Tom,

On Mon, February 12, 2018 5:03 pm, Tom Lane wrote:
> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> 2018-02-09 12:02 GMT+01:00 Marko Tiikkaja <marko(at)joh(dot)to>:
>>> This is quite short-sighted. The better way to do this is to complain
>>> if
>>> the number of expressions is different from the number of target
>>> variables
>>> (and the target variable is not a record-ish type). There's been at
>>> least
>>> two patches for this earlier (one my me, and one by, I think Pavel
>>> Stehule). I urge you to dig around in the archives to avoid wasting
>>> your
>>> time.
[snip a bit]

> As things stand today, we would have a hard time tightening that up
> without producing unwanted complaints about the cases mentioned in
> this comment, because the DTYPE_ROW logic is used for both "INTO a,b,c"
> and composite-type variables. However, my pending patch at
> https://commitfest.postgresql.org/17/1439/
> gets rid of the use of DTYPE_ROW for composite types, and once that
> is in it might well be reasonable to just throw a flat-out error for
> wrong number of source values for a DTYPE_ROW target. I can't
> immediately think of any good reason why you'd want to allow for
> the number of INTO items not matching what the query produces.

Perl lets you set a fixed number of multiple variables from an array and
discard the rest like so:

my ($a, $b) = (1,2,3);

and the right hand side can also be a function:

my ($c, $d) = somefunc( 123 );

Where somefunc() returns more than 2 params.

This is quite handy if you sometimes need more ore less return values, but
don't want to create almost-identical functions for each case.

I'm not sure if you mean exactly the scenario as in the attached test
case, but this works in plpgsql, too, and would be a shame to lose.

OTOH, one could also write:

SELECT INTO ba, bb a,b FROM foo(1);

and it would still work, or wouldn't it?

Best regards,

Tels