Computing SUM on DATETIME datatype

hi everybody,
i'm trying to calculate the 'SUM' of time spent in hrs. n min. How can i do this using SQL Server?
What i mean is, i've a column 'TIME_SPENT' that has 'datetime' datatype. This column saves time spent for an activity in format 'hh:mm'. Suppose a user spends 45min for activity 'A' and say 1hr 25 min for activity 'B' then i want to calculate the 'SUM' of 'TIME_SPENT' for the user which should appear as 'Total time spent =2:10'

Can somebody pls help me with this?

Thnx in advance.create table #timetable (username varchar(50),timespend varchar(8))

insert into #timetable values ('joe','03:01')
insert into #timetable values ('joe','00:01')
insert into #timetable values ('foo','00:03')
insert into #timetable values ('foo','01:02')



select username,
convert(varchar(5),dateadd(second,sum(datediff(sec ond,'19000101','1900-01-01T'+timespend+':00')),'19000101'),8)
as t_timespend
from #timetable
group by username|||hey thnx for ur reply mallier,

ur code works great for the example u explained. But when i try to run it for my table in the database it gives following error:-
'The conversion of a char data type to a datetime data type resulted in an out-of-range datetime value.'

My code goes as follows:-

select empid,
convert(varchar(5),dateadd(second,sum(datediff(sec ond,'19000101','1900-01-01T'+time_spent+':00')),'19000101'),8) as 'Time spent'
from timesheet
where empid=9
group by empid
can u pls guide me on this?

thnx once again.|||try this select query on ur table (I hope data is in 'hh:mm' format)


create table #timetable (username varchar(50),timespend char(8))

insert into #timetable values ('joe','03:01')
insert into #timetable values ('joe','00:01')
insert into #timetable values ('foo','00:03')
insert into #timetable values ('foo','01:02')



select username,case when days>0 then cast(days*24+cast(left(times,2) as int)as varchar)+':'+right(times,2)
else
times
end as total_time
from
(
select username,
datediff(day,'19000101',dateadd(second,sum(datedif f(second,'19000101','1900-01-01T'+ltrim(rtrim(timespend))+':00')),'19000101'))
as days,
convert(varchar(5),dateadd(second,sum(datediff(sec ond,'19000101','1900-01-01T'+ltrim(rtrim(timespend))+':00')),'19000101'),8 ) as times
from #timetable
group by username
) as tm|||create table #babu ( names varchar(10),times varchar(10))

insert into #babu values ('babu0','01:20')
insert into #babu values ('babu1','01:20')
insert into #babu values ('babu1','01:20')
insert into #babu values ('babu0','01:20')
insert into #babu values ('babu0','01:20')

select names, dateadd(second,sum(datediff(second,'1900-01-01',convert(datetime,times))),'1900-01-01') from #babu group by names|||create table #babu ( names varchar(10),times varchar(10))

insert into #babu values ('babu0','01:20')
insert into #babu values ('babu1','01:20')
insert into #babu values ('babu1','01:20')
insert into #babu values ('babu0','01:20')
insert into #babu values ('babu0','01:20')


select names, dateadd(second,sum(datediff(second,'1900-01-01',convert(datetime,times))),'1900-01-01') from #babu group by namesthat wont help him,b'cos datatype of time column is char and he dont want see the date value too.