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

On Sun, Feb 18, 2024 at 7:29 AM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
>
>
> Also, now that I looked at the v2 patch again, I see it only really
> tweaked the pg_proc.dat entry, but the code still does PG_GETARG_OID (so
> the "any" bit is not really correct).
>

PG_GETARG_OID part indeed is wrong. so I change to following:

+Datum
+pg_basetype(PG_FUNCTION_ARGS)
+{
+ Oid oid;
+
+ oid =  get_fn_expr_argtype(fcinfo->flinfo, 0);
+ if (!SearchSysCacheExists1(TYPEOID, ObjectIdGetDatum(oid)))
+ PG_RETURN_NULL();
+
+ PG_RETURN_OID(getBaseType(oid));
+}

I still name the function as pg_basetype, feel free to change it.

+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_basetype</primary>
+        </indexterm>
+        <function>pg_basetype</function> ( <type>"any"</type> )
+        <returnvalue>regtype</returnvalue>
+       </para>
+       <para>
+       Returns the OID of the base type of a domain or if the
argument is a basetype it returns the same type.
+       If there's a chain of domain dependencies, it will recurse
until finding the base type.
+       </para>
compared with pg_typeof's explanation, I feel like pg_basetype's
explanation doesn't seem accurate.
However, I don't know how to rephrase it.