declare @tab1 table(userid int, tt time)
declare @tab2 table(userid int, tt time)
insert into @tab1
select 1, '00:00:06' union all
select 1, '00:05:00'
insert into @tab2
select 1, '01:05:06'
;with cte1 as(
select userid, sum((DATEPART(hh, tt) * 60*60) + (DATEPART(mi, tt) * 60) + DATEPART(ss, tt)) secs from @tab1 group by userid
), cte2 as(
select userid, sum((DATEPART(hh, tt) * 60*60) + (DATEPART(mi, tt) * 60) + DATEPART(ss, tt)) secs from @tab2 group by userid
)
select userid, cast(cast(secs/(3600) as varchar) + ':' + cast((secs%3600)/60 as varchar) + ':' + cast(secs%60 as varchar) as time)as tt
from (
select a.userid, a.secs-b.secs as secs
from cte2 a
left join cte1 b on a.userid = b.userid
) tab