DATEDIFF in HH:MM:SS format

Question

I need to calculate the total length in terms of Hours, Minutes, Seconds, and the average length, given some data with start time and end time.

For example the resul

Answer 1

SELECT CONVERT(time, 
               DATEADD(mcs, 
                       DATEDIFF(mcs, 
                                '2007-05-07 09:53:00.0273335', 
                                '2007-05-07 09:53:01.0376635'), 
                       CAST('1900-01-01 00:00:00.0000000' as datetime2)
                      )
              )