如何在查询中的查询中使用ISNULL？

现在我的SQL查询正确地返回RoomsAvailable字段，除非采用0房间，其中SQL命令用NULL减去number_of_rooms并将NULL输出到列。我尝试了很多ISNULL版本，发现它不起作用;任何人都知道我应该如何做到这一点？如何在查询中的查询中使用ISNULL？

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

电流输出：

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

来源

2011-10-17 user971537

为什么你有SELECT COUNT的SELECT DISTINCT？如果您的查询返回多条记录，则可能会出现错误，并且您的计算不起作用。 – vol7ron

你的意思是这个？：

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

或者是，你得到NULL在所有问题？在那种情况下，我会怀疑你的JOIN可能有问题。

你可以围绕任何包装一个ISNULL嵌套的子查询或值。

来源

2011-10-17 22:59:22 Matthew

嗨，我意识到这是多么愚蠢，我仍然是NULL，我现在正在寻找联接。 – user971537

如何在查询中的查询中使用ISNULL？

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