SQL query to search for room availability

Question

The follow tables I have are:

 CUSTOMERS (CustomerID, firstname, surname etc)
 ROOMS (RoomID, RoomType, Description)
 BOOKING (BookingID, CustomerID, Arriva         


        

Answer 1

You have the following cases

The user's selected period:
--------[---------]-------
Booking no1 
[-----]-------------------
Booking no2
--------------------[----]
Booking no3
-----[----]---------------
Booking no4
-----------[---]----------
Booking no5
------[-------]-----------
Booking no6
--------------[--------]--
Booking no7
-----[----------------]---

You will have to find which periods cross over. Obviously cases 1 and 2 are free. Cases 3,5,6 are easy to catch as you can search if either the start date of the booking or the end date of the booking is within the user's selection. Cases 4 and 7 you would need to find if either of the user's selection dates would be between the bookings.

So the following finds free rooms:

DECLARE @ArrivalDate AS DATETIME
DECLARE @DepartureDate AS DATETIME

SELECT RoomType 
FROM ROOMS 
WHERE RoomID NOT IN 
(
    SELECT RoomID 
    FROM   BOOKING B
           JOIN ROOMS_BOOKED RB
               ON B.BookingID = RB.BookingID
    WHERE  (ArrivalDate <= @ArrivalDate AND DepartureDate >= @ArrivalDate) -- cases 3,5,7
           OR (ArrivalDate < @DepartureDate AND DepartureDate >= @DepartureDate ) --cases 6,6
           OR (@ArrivalDate <= ArrivalDate AND @DepartureDate >= ArrivalDate) --case 4
)