Fact Function to find Factorial

CREATE OR REPLACE FUNCTION fact(n INTEGER)
RETURNS INTEGER AS $$
DECLARE
	b INTEGER := 1;
	i INTEGER;
BEGIN
	IF n < 0 THEN
		RAISE EXCEPTION 'Factorial is not defined for negative numbers';
	END IF;

	FOR i IN 1..n LOOP
		b := b * i;
	END LOOP;

	RETURN b;
END;

$$ LANGUAGE plpgsql;