a sample postgresql function

car_bonus.sql

CREATE FUNCTION car_bonus_func(vehicle_id int, bonus int)
RETURNS cars
AS $$
DECLARE
  car cars;
BEGIN
 PERFORM model FROM cars WHERE car_id = vehicle_id;
 IF NOT FOUND THEN
    RAISE EXCEPTION 'car with id of % not found', vehicle_id;
END IF;

IF bonus > 13 THEN
   RAISE EXCEPTION 'sales bonus cannot be greater than 13';
END IF;

 UPDATE cars SET sales_bonus = bonus
        WHERE car_id = vehicle_id;
 SELECT * INTO car FROM cars WHERE car_id = vehicle_id;
 RETURN car;
END;
$$
LANGUAGE plpgsql;