Question

My SQL Query below is now Returning the RoomsAvailable field correctly except when theres 0 rooms taken, in which the SQL command subtracts number_of_rooms with NULL and outputs NULL to the Column. I have tried numerous ISNULL variations and found that it doesnt work; anyone know how I should be doing this?

SQL :

SELECT
    Hotel_2.hotel_code, 
    Hotel_2.hotel_country, 
    Room_type_rates_2.room_type_code, 
    Room_type_rates_2.number_of_rooms, 
    Types_2.room_type, 
    Room_type_rates_2.rates, 
            Room_type_rates_2.number_of_rooms -
            (SELECT 
                DISTINCT (SELECT
                             COUNT(dbo.Hotel.hotel_code) AS RoomsTake
                          FROM
                              dbo.Hotel 
                          INNER JOIN dbo.Hotel_Reservation 
                              ON dbo.Hotel.hotel_code = dbo.Hotel_Reservation.hotel_code 
                          INNER JOIN dbo.Room_type_rates 
                              ON dbo.Hotel.hotel_code = dbo.Room_type_rates.hotel_code 
                          INNER JOIN dbo.Types 
                              ON dbo.Hotel_Reservation.room_type_code = dbo.Types.room_type_code 
                              AND dbo.Room_type_rates.room_type_code = dbo.Types.room_type_code
                          WHERE
                              (dbo.Room_type_rates.room_type_code = Room_type_rates_1.room_type_code) 
                              AND (dbo.Hotel.hotel_code = Hotel_1.hotel_code)
                              AND (dbo.Hotel_Reservation.checkin_date >= Hotel_Reservation_1.checkin_date)
                              AND (dbo.Hotel_Reservation.checkout_date <= Hotel_Reservation_1.checkout_date)
                          ) AS RoomsTaken
               FROM
                   dbo.Hotel AS Hotel_1 
               INNER JOIN dbo.Hotel_Reservation AS Hotel_Reservation_1
                   ON Hotel_1.hotel_code = Hotel_Reservation_1.hotel_code 
               INNER JOIN dbo.Room_type_rates AS Room_type_rates_1 
                   ON Hotel_1.hotel_code = Room_type_rates_1.hotel_code 
               INNER JOIN dbo.Types AS Types_1 
                   ON Hotel_Reservation_1.room_type_code = Types_1.room_type_code 
                   AND Room_type_rates_1.room_type_code = Types_1.room_type_code
               WHERE
                   (Hotel_Reservation_1.checkin_date >= '11/19/2011') 
                   AND (Hotel_Reservation_1.checkout_date <= '12/01/2011') 
                   AND (Hotel_1.hotel_country = 'Adelaide') 
                   AND (Types_1.room_type_code = Types_2.room_type_code)
               ) AS RoomsAvailable 
FROM 
    dbo.Hotel AS Hotel_2 
INNER JOIN dbo.Room_type_rates AS Room_type_rates_2 
    ON Hotel_2.hotel_code = Room_type_rates_2.hotel_code 
INNER JOIN dbo.Types AS Types_2 
    ON Room_type_rates_2.room_type_code = Types_2.room_type_code

Current Output :


ADL20 Adelaide CPL 6 Couple Suite 514.0000 3

ADL20   Adelaide    FYU         3   Family Suite    533.0000    2

ADL20   Adelaide    KNG         2   King's Bedroom  556.0000    NULL

Answer 1

Do you mean this?:

...ISNULL(COUNT(dbo.Hotel.*),0)...

Or is the problem that you’re getting NULL at all? In that case I would suspect your JOINs may have a problem.

You can wrap an ISNULL around any nested subquery or value.