Re: Add pg_basetype() function to obtain a DOMAIN base type

On Mon, Mar 18, 2024 at 11:43 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Alexander Korotkov <aekorotkov(at)gmail(dot)com> writes:
> > On Mon, Mar 18, 2024 at 2:01 AM jian he <jian(dot)universality(at)gmail(dot)com> wrote:
> >> `
> >> Datum
> >> pg_basetype(PG_FUNCTION_ARGS)
> >> {
> >> Oid oid;
> >>
> >> oid = get_fn_expr_argtype(fcinfo->flinfo, 0);
> >> PG_RETURN_OID(getBaseType(oid));
> >> }
> >> `
>
> > Looks good to me. But should it be named pg_basetypeof()?
>
> I still don't like this approach. It forces the function to be
> used in a particular way that's highly redundant with pg_typeof.
> I think we'd be better off with
>
> pg_basetype(PG_FUNCTION_ARGS)
> {
> Oid typid = PG_GETARG_OID(0);
>
> PG_RETURN_OID(getBaseType(typid));
> }
>
> The use-case that the other definition handles would be implemented
> like
>
> pg_basetype(pg_typeof(expression))
>

trying to do it this way.
not sure the following error message is expected.

SELECT pg_basetype(-1);
ERROR: cache lookup failed for type 4294967295