Function build_aggregate_finalfn_expr

src/backend/parser/parse_agg.c:2187–2218

* Like build_aggregate_transfn_expr, but creates an expression tree for the * final function of an aggregate, rather than the transition function. */

 * final function of an aggregate, rather than the transition function.
 */
void
build_aggregate_finalfn_expr(Oid *agg_input_types,
							 int num_finalfn_inputs,
							 Oid agg_state_type,
							 Oid agg_result_type,
							 Oid agg_input_collation,
							 Oid finalfn_oid,
							 Expr **finalfnexpr)
{
	List	   *args;
	int			i;

	/*
	 * Build expr tree for final function
	 */
	args = list_make1(make_agg_arg(agg_state_type, agg_input_collation));

	/* finalfn may take additional args, which match agg's input types */
	for (i = 0; i < num_finalfn_inputs - 1; i++)
	{
		args = lappend(args,
					   make_agg_arg(agg_input_types[i], agg_input_collation));
	}

	*finalfnexpr = (Expr *) makeFuncExpr(finalfn_oid,
										 agg_result_type,
										 args,
										 InvalidOid,
										 agg_input_collation,
										 COERCE_EXPLICIT_CALL);
	/* finalfn is currently never treated as variadic */
}

/*
 * Convenience function to build dummy argument expressions for aggregates.