SQL calculate time difference between two rows containing specific values

Question

I have a table that contains information of a users work status on a mobile device. Every time their status changes, a new row is created, with their original status before the change, and what their new status now is. The table looks like this:

ID      Date_Time              User      OriginalStatus     NewStatus    
---------------------------------------------------------------------------
60713   2017-04-11 12:14:42    Helen     Not Started        Active
60714   2017-04-11 12:19:20    Monica    Active             Paused
60715   2017-04-11 12:20:43    Dave      Active             Paused
60716   2017-04-11 12:32:18    Helen     Finished           Archived
60717   2017-04-11 12:48:57    Monica    Paused             Active
60718   2017-04-11 12:52:35    Dave      Paused             Active

What I am trying to do is calculate the duration that each user remains in the 'Paused' status on each date... they are only allowed to move from 'Paused' back to 'Active' which denotes the end of their 'Paused' time, and all other rows can be ignored, and the changes from 'Paused' back to 'Active' will not be in consecutive rows.

In the above example, Monica has remained 'Paused' for 29 minutes and 37 Seconds (12:19:20 to 12:48:57) and Dave has been 'Paused' for 31 minutes and 52 seconds (12:20:43 to 12:52:35).

Ideally I'd like results similar to:

User      Paused_Start_Time      Paused_End_Time        Paused_Duration
---------------------------------------------------------------------------
Monica    2017-04-11 12:19:20    2017-04-11 12:48:57    00:29:37
Dave      2017-04-11 12:20:43    2017-04-11 12:52:35    00:31:52

I'm at a loss to how to go about working this out, so all help gratefully received. I'm using SQL Server 2012.

Answer 1

I think you just need lead() :

select user, date_time as paused_starttime, next_date_time as paused_endtime
from (select t.*,
             lead(date_time) over (partition by user order by date_time) as next_date_time
      from t
     ) t
where status = 'paused';

To get the duration you can subtract the values. However, this returns the interval as a datetime value. You can convert this to a time , but the time will never be greater than 24 hours. I'm not sure what you want to do when the time exceeds that period.