Find free room (booking system)

Question

For a booking system I have a table with rooms, arrival and departure.

Example data:

id | room | arrival    | departure
---+------+------------+-----         


        

Answer 1

Here is a query that will show the NOT-FREE rooms for a date span:

select room from bookings where
(arrival<'2011-03-12' and departure>='2011-03-12') -- overlap at the end
OR (arrival<='2011-03-10' and departure>'2011-03-10') -- overlap at the start
OR (arrival>='2011-03-10' and departure<='2011-03-12') -- complete overlap

You can use this with

select roomnumber from rooms where roomnumber not in (... as above ...)

to find the FREE rooms

Answer 2

You could also use the BETWEEN comparison operator for this purpose. In this case you would do something like this:

SELECT r.id FROM room r WHERE r.id NOT IN
(
    SELECT rb.room FROM room_booking rb WHERE 
        ('2011-03-10' BETWEEN rb.arrival AND rb.departure) OR 
        ('2011-03-12' BETWEEN rb.arrival AND rb.departure)
)