Function finalize_grouping_exprs_walker

src/backend/parser/parse_agg.c:1565–1706

}

static bool
finalize_grouping_exprs_walker(Node *node,
							   check_ungrouped_columns_context *context)
{
	ListCell   *gl;

	if (node == NULL)
		return false;
	if (IsA(node, Const) ||
		IsA(node, Param))
		return false;			/* constants are always acceptable */

	if (IsA(node, Aggref))
	{
		Aggref	   *agg = (Aggref *) node;

		if ((int) agg->agglevelsup == context->sublevels_up)
		{
			/*
			 * If we find an aggregate call of the original level, do not
			 * recurse into its normal arguments, ORDER BY arguments, or
			 * filter; GROUPING exprs of this level are not allowed there. But
			 * check direct arguments as though they weren't in an aggregate.
			 */
			bool		result;

			Assert(!context->in_agg_direct_args);
			context->in_agg_direct_args = true;
			result = finalize_grouping_exprs_walker((Node *) agg->aggdirectargs,
													context);
			context->in_agg_direct_args = false;
			return result;
		}

		/*
		 * We can skip recursing into aggregates of higher levels altogether,
		 * since they could not possibly contain exprs of concern to us (see
		 * transformAggregateCall).  We do need to look at aggregates of lower
		 * levels, however.
		 */
		if ((int) agg->agglevelsup > context->sublevels_up)
			return false;
	}

	if (IsA(node, GroupingFunc))
	{
		GroupingFunc *grp = (GroupingFunc *) node;

		/*
		 * We only need to check GroupingFunc nodes at the exact level to
		 * which they belong, since they cannot mix levels in arguments.
		 */

		if ((int) grp->agglevelsup == context->sublevels_up)
		{
			ListCell   *lc;
			List	   *ref_list = NIL;