Hi

I have been asked to provide the time between cases (Turn Around) in a report and I'm stuck, I have no idea where to begin with the SQL query.
We have a single table in a database that holds patient records including the start and end of each operation and session identifiers (Theatre, Date & Session ID).
What I need to do is show how much time is being wasted between cases. The data in the table is held in the format

Theatre   Date      SessionId   PatientId  Start  Finish
Th1       1/3/2009   TH1AM      P332233    8:30   9:00
Th1       1/3/2009   TH1AM      P123223    9:15  10:00
Th1       1/3/2009   TH1AM      P339888   10:30  11:30
Th1       1/3/2009   TH1AM      P339999   11:35  11:50
Th2       1/3/2009   TH2AM      P776666    8:40  10:00
Th2       1/3/2009   TH2AM      P887772   11:30  12:00


what I want to do is produce a report in the following format, with the last column showing the amount of time between the cases (Turn Around Time)


Th1   1/3/2009   TH1AM   P332233    8:30    9:00
Th1   1/3/2009   TH1AM   P123223    9:15   10:00    0:15
Th1   1/3/2009   TH1AM   P339888   10:30   11:30    0:30
Th1   1/3/2009   TH1AM   P339999   11:35   11:50    0:05

Th2   1/3/2009   TH2AM   P776666    8:40  10:00
Th2   1/3/2009   TH2AM   P887772   11:30  12:00     1:30

Any help gratefully appreciated

Thanks