CREATE TRIGGER reduceSalary

    BEFORE UPDATE OF salary ON person

    FOR EACH ROW

    WHEN (NEW.salary < OLD.salary)

    DECLARE

       lessMoney EXCEPTION;

    BEGIN

       RAISE lessMoney;

       EXCEPTION

         WHEN lessMoney THEN

           raise_application_error(-20001,'Attempt to reduce salary. Rejected!');

    END;



CREATE FUNCTION reduce_salary() RETURNS TRIGGER AS $reduceSalary$
BEGIN
	IF NEW.salary < OLD.salary THEN
		RAISE EXCEPTION 'Salary cannot be reduced';
	END IF;
	RETURN NEW;
END;
$reduceSalary$ LANGUAGE plpgsql;

CREATE TRIGGER reduceSalary
BEFORE UPDATE ON person
FOR EACH ROW EXECUTE PROCEDURE reduce_salary();