Tuning a loop statement

Hi,
If someone would be able to help me cut down the execution time on this piece of code I would be most greatful. In the [NEMTIME] table I've got a list of every halfhour from the start of 2004 through the end of 2011. I'm trying to get the sum of the another field in table [master contracts] where the dates in the [NEMTIME] are between the dates in the [master contracts] table.
It takes about 20mins to return a result. It would help me alot if I could cut this time down.declare
@theTime datetime -- the current interval to assessdeclare
@maxTime datetime -- maximum date interval in nemtimeselect
@theTime = min(nemtime) from nemtimeselect
@maxTime = max(nemtime) from nemtime -- while the current time is less than the latest datewhile
@theTime <= @maxTimebegin
-- cover is the name of the 2nd column in the nemtime tableupdate nemtime
-- set the total volume to the sum between the start and end datesset cover = (select sum(volume) from [Contract Master] where @theTime >= start_date and @theTime <= end_date)
where nemtime = @theTime
-- add 30 minutes to obtain the next interval and repeat
select @theTime = dateadd(mi, 30, @theTime)end

Hi,
I have understood your query correctly then I feel you dont need this loop at all.
Copy this sample code along with row data and run in QA to check the desired result:declare
@t1 table(thetime datetime,cover int)insert
@t1(thetime) select
'2007-12-14 00:00:00' union all select
'2007-12-14 00:30:00' union all select
'2007-12-14 01:00:00' union all select
'2007-12-14 01:30:00' union all select
'2007-12-14 02:00:00' union all select
'2007-12-14 02:30:00' union all select
'2007-12-14 03:00:00' union all select
'2007-12-14 03:30:00' declare
@t2 table(startdate datetime,enddate datetime,volume int)insert
@t2select
'2007-12-14 00:25:00','2007-12-14 00:45:00',5 union all select
'2007-12-14 00:29:00','2007-12-14 00:39:00',4 union all select
'2007-12-14 00:59:00','2007-12-14 01:00:00',3 union all select
'2007-12-14 01:20:00','2007-12-14 01:40:00',7 union all select
'2007-12-14 01:30:00','2007-12-14 01:57:00',6 union all select
'2007-12-14 02:30:00','2007-12-14 02:30:00',4 union all select
'2007-12-14 02:49:00','2007-12-14 03:09:00',12 union all select
'2007-12-14 02:50:00','2007-12-14 00:10:00',90 select
thetime,sum(volume) from @t1 t1 join @t2 t2 ONt1
.thetime between t2.startdate and t2.enddategroup
by thetime