Function GetNSItemByRangeTablePosn

src/backend/parser/parse_relation.c:498–519

* Given an RT index and nesting depth, find the corresponding * ParseNamespaceItem (there must be one). */

 * ParseNamespaceItem (there must be one).
 */
ParseNamespaceItem *
GetNSItemByRangeTablePosn(ParseState *pstate,
						  int varno,
						  int sublevels_up)
{
	ListCell   *lc;

	while (sublevels_up-- > 0)
	{
		pstate = pstate->parentParseState;
		Assert(pstate != NULL);
	}
	foreach(lc, pstate->p_namespace)
	{
		ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(lc);

		if (nsitem->p_rtindex == varno)
			return nsitem;
	}
	elog(ERROR, "nsitem not found (internal error)");
	return NULL;				/* keep compiler quiet */
}

/*
 * Given an RT index and nesting depth, find the corresponding RTE.