HELP with a DATETIME Query

I have a table called Bookings which has two important columns; Booking_Start_Date and Booking_End_Date. These columns are both of type DATETIME. The following query calculates how many hours are available between the hours of 09.00 and 17.30 so a user can see at a glance how many hours they have unbooked on a particular day (i.e. 8.5 hours less the time of any bookings on that day). However, when a booking spans more than one day the query doesn't work, for example if a user has a booking that starts on day one at 09.00 and ends at 14.30 on the next day, the query returns 3.5 hours for both days. Any help here would be greatly appreciated.

SELECT 8.5 - (SUM(((DATE_FORMAT(B.Booking_End_Date, '%k') * 60 ) + DATE_FORMAT(B.Booking_End_Date, '%i')) - ((DATE_FORMAT(B.Booking_Start_Date, '%k') * 60 ) + DATE_FORMAT(B.Booking_Start_Date, '%i'))) / 60) AS Available_Hours FROM WMS_Bookings B WHERE B.User_ID = '16' AND B.Booking_Status <> '1' AND NOT ( '2003-10-07' < DATE_FORMAT(Booking_Start_Date, "%Y-%m-%d") OR '2003-10-07' > DATE_FORMAT(Booking_End_Date, "%Y-%m-%d") )

Thanks for your help Received on Sun Oct 05 2003 - 22:48:47 CEST