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

[Tom Lane]

Alexander Korotkov <aekorot...@gmail.com> writes:
> On Mon, Mar 18, 2024 at 2:01 AM jian he <jian.universal...@gmail.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))

but there are other use-cases.  For example, if you want to know
the base types of the columns of a table, you could do something
like

select attname, pg_basetype(atttypid) from pg_attribute
  where attrelid = 'foo'::regclass order by attnum;

but that functionality is simply not available with the other
definition.

Perhaps there's an argument for providing both things, but that
feels like overkill to me.  I doubt that pg_basetype(pg_typeof())
is going to be so common as to need a shorthand.

                        regards, tom lane