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

On Mon, Mar 18, 2024 at 2:01 AM jian he <jian.universality@gmail.com> wrote:
>
> looking at it again.
> I found out we can just simply do
> `
> Datum
> pg_basetype(PG_FUNCTION_ARGS)
> {
> Oid oid;
>
> oid =  get_fn_expr_argtype(fcinfo->flinfo, 0);
> PG_RETURN_OID(getBaseType(oid));
> }
> `
>
> if the type is not a domain, work the same as  pg_typeof.
> if the type is domain,  pg_typeof return as is, pg_basetype return the
> base type.
> so it only diverges when the argument type is a type of domain.
>
> the doc:
>         <function>pg_basetype</function> ( <type>"any"</type> )
>         <returnvalue>regtype</returnvalue>
>        </para>
>        <para>
>        Returns the OID of the base type of a domain. If the argument
> is not a type of domain,
>        return the OID of the data type of the argument just like <link
> linkend="function-pg-typeof"><function>pg_typeof()</function></link>.
>        If there's a chain of domain dependencies, it will recurse
> until finding the base type.
>        </para>
>
>
> also, I think this way, we only do one syscache lookup.

Looks good to me.  But should it be named pg_basetypeof()?

------
Regards,
Alexander Korotkov