MySql根据前一行值计算行数

Question

CREATE PROCEDURE available_rooms(
hotelname_param VARCHAR(45),
date_param  DATE)
BEGIN

IF date_param IS NULL  THEN -- if the booking date is null
    SIGNAL SQLSTATE '22003' -- signalling error
    SET MESSAGE_TEXT = 'the booing date should not be null',
    MYSQL_ERRNO = 1264;
END IF;

SELECT h.Hotel_id AS HotelID,hotelname_param AS HotelName,((h.Floor_count) * (h.Roomsperfloor)) AS TotalRooms,
    g.Guest_firstname AS Guestname,b.Room_count AS RoomsBooked,
    (((h.Floor_count) * (h.Roomsperfloor)) - b.Room_count) AS AvailableRooms 
FROM hotel h
JOIN guests g ON h.Hotel_id = g.Hotel_id
JOIN booking b ON g.Guest_id = b.Guest_id
WHERE b.BookingDate = date_param;
END

CALL available_rooms（'Grand Central Inn'，'2018-01-11'）

当我调用该过程时，其显示输出为THIS 因此，第一行的可用房间应该用于下一行计算，但我无法得到它。任何人都可以帮助我