I've got the following trigger;

CREATE TRIGGER trFLightAndDestination
ON checkin_flight
AFTER INSERT,UPDATE
AS
BEGIN
    IF NOT EXISTS
    (
                    SELECT 1 
            FROM Flight v
            INNER JOIN Inserted AS i ON i.flightnumber = v.flightnumber
            INNER JOIN checkin_destination AS ib ON ib.airport = v.airport
            INNER JOIN checkin_company AS im ON im.company = v.company
            WHERE i.desk = ib.desk AND i.desk = im.desk
    )
    BEGIN
        RAISERROR('This combination of of flight and check-in desk is not possible',16,1)
        ROLLBACK TRAN       
    END
END

What i want the trigger to do is to check the tables Flight, checkin_destination and checkin_company when a new record for checkin_flight is added. Every record of checkin_flight contains a flightnumber and desknumber where passengers need to check in for this destination. The tables checkin_destination and checkin_company contain information about companies and destinations restricted to certain checkin desks. When adding a record to checkin_flight i need information from the flight table to get the destination and flightcompany with the inserted flightnumber. This information needs to be checked against the available checkin combinations for flights, destinations and companies.

I'm using the trigger as stated above, but when i try to insert a wrong combination the trigger allows it. What am i missing here?