Continuous columns sum based on another column in sql server

Question

I have data like below

AppName	Start	Finish	Totaltime
MS Word	2021-02-28 7:30:25	2021-02-28 7:31:25	1
MS Word	2021-02-28 7:31:26	2021-02-28 7:33:25	2
MS Word	2021-02-28 7:33:27	2021-02-28 7:35:25	2
MS Word	2021-02-28 7:35:28	2021-02-28 7:37:25	2
Google Chrome	2021-02-28 7:37:29	2021-02-28 7:39:25	2
Windows Explorer	2021-02-28 7:39:30	2021-02-28 7:41:25	2
Windows Explorer	2021-02-28 7:41:31	2021-02-28 7:43:25	2
MS Word	2021-02-28 7:43:32	2021-02-28 7:45:25	2
MS Word	2021-02-28 7:45:33	2021-02-28 7:47:25	2
Google Chrome	2021-02-28 7:47:34	2021-02-28 7:49:25	2
Google Chrome	2021-02-28 7:49:35	2021-02-28 7:51:25	2
Google Chrome	2021-02-28 7:51:36	2021-02-28 7:53:25	2
Microsoft Excel	2021-02-28 7:53:37	2021-02-28 7:55:25	2

and need the coninuoues column Totaltime sum based on App name

output something like this

AppName	Start	Finish	Totaltime
MS Word	2021-02-28 7:30:25	2021-02-28 7:37:25	7
Google Chrome	2021-02-28 7:37:29	2021-02-28 7:39:25	2
Windows Explorer	2021-02-28 7:39:30	2021-02-28 7:43:25	4
MS Word	2021-02-28 7:43:32	2021-02-28 7:47:25	4
Google Chrome	2021-02-28 7:47:34	2021-02-28 7:53:25	6
Microsoft Excel	2021-02-28 7:53:37	2021-02-28 7:55:25	2

Answer 1

This is a type of gaps and islands problem. You don't care about the time gaps in the table, so you can use the difference of row numbers:

select appname, min(start), max(finish), sum(time)
from (select t.*,
             row_number() over (order by start) as seqnum,
             row_number() over (partition by appname order by start) as seqnum_a
      from t
     ) t
group by appname, (seqnum - seqnum_a)