Do I need a while loop?

Hello

I have the following SQL which returns a time a person was in a particular department

select
Loc_name,
ROW_NUMBER() OVER(ORDER BY LocationDate) as RowNum,
CONVERT(varchar, Location_Date - Arrival_Date),108) as Time
from dbo.locations
where attendance_id = '123456'

I get results as follows:

Arrival Date Location Date RowNum Time Location
26/02/2013 19:13 26/02/2013 19:20 1 00:07:00 Queue 1
26/02/2013 19:13 26/02/2013 19:30 2 00:17:00 Dept 1
26/02/2013 19:13 26/02/2013 21:10 3 01:57:00 Dept 2
26/02/2013 19:13 27/02/2013 02:50 4 07:37:00 Left Department

What I want to achieve is bypass the 01:57 and show 07:37 as the time the person spent in Dept2? If the last Location is "Left Department" then I only want to show the previous department in the location field

I.e.


Arrival Date Location Date RowNum Time Location
26/02/2013 19:13 26/02/2013 19:20 1 00:07:00 Queue1
26/02/2013 19:13 26/02/2013 19:30 2 00:17:00 Dept1
26/02/2013 19:13 27/02/2013 02:50 3 07:37:00 Dept2



Do I need a while loop to achieve this? and if so, could someone kindly help me get started with this as I am unsure of the syntex to write

Other suggestions are very welcome

Kind Regards