Re: polymorphic SQL functions has a problem with domains

2014-04-02 17:19 GMT+02:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> > I was informed about impossibility to use a polymorphic functions
> together
> > with domain types
>
> > see
>
> > create domain xx as numeric(15);
>
> > create or replace function g(anyelement, anyelement)
> > returns anyelement as
> > $$ select $1 + $2 $$
> > language sql immutable;
>
> > postgres=# select g(1::xx, 2::xx);
> > ERROR: return type mismatch in function declared to return xx
> > DETAIL: Actual return type is numeric.
> > CONTEXT: SQL function "g" during inlining
>
> That example doesn't say you can't use polymorphic functions with domains.
> It says that this particular polymorphic function definition is wrong:
> it is not making sure its result is of the expected data type. I don't
> recall right now whether SQL functions will apply an implicit cast on the
> result for you, but even if they do, an upcast from numeric to some domain
> over numeric wouldn't be implicit.
>

I though about this issue again, and I am thinking so it is PostgreSQL bug

we can do safe transformation from Parent type -> domain.

and returning result require same transformation (in this case) - so
enforcing casting (not only binary casting) should be safe.

Otherwise - CAST(var AS var) should be useful and can helps too.

Regards

Pavel Stehule

>
> regards, tom lane
>