Calculate a Running Total in SQL Server

Question

Imagine the following table (called TestTable):

id     somedate    somevalue
--     --------    ---------
45     01/Jan/09   3
23     08/Jan/09   5
12     02/Feb/09   0
77     14/Feb/09   7
39     20/Feb/09   34
33     02/Mar/09   6

I would like a query that returns a running total in date order, like:

id     somedate    somevalue  runningtotal
--     --------    ---------  ------------
45     01/Jan/09   3          3
23     08/Jan/09   5          8
12     02/Feb/09   0          8
77     14/Feb/09   7          15  
39     20/Feb/09   34         49
33     02/Mar/09   6          55

I know there are various ways of doing this in SQL Server 2000 / 2005 / 2008.

I am particularly interested in this sort of method that uses the aggregating-set-statement trick:

INSERT INTO @AnotherTbl(id, somedate, somevalue, runningtotal) 
   SELECT id, somedate, somevalue, null
   FROM TestTable
   ORDER BY somedate

DECLARE @RunningTotal int
SET @RunningTotal = 0

UPDATE @AnotherTbl
SET @RunningTotal = runningtotal = @RunningTotal + somevalue
FROM @AnotherTbl

... this is very efficient but I have heard there are issues around this because you can't necessarily guarantee that the UPDATE statement will process the rows in the correct order. Maybe we can get some definitive answers about that issue.

But maybe there are other ways that people can suggest?

edit: Now with a SqlFiddle with the setup and the 'update trick' example above

Answer 1

Though best way is to get it done will be using a window function, it can also be done using a simple correlated sub-query.

Select id, someday, somevalue, (select sum(somevalue) 
                                from testtable as t2
                                where t2.id = t1.id
                                and t2.someday <= t1.someday) as runningtotal
from testtable as t1
order by id,someday;

Answer 2

The APPLY operator in SQL 2005 and higher works for this:

select
    t.id ,
    t.somedate ,
    t.somevalue ,
    rt.runningTotal
from TestTable t
 cross apply (select sum(somevalue) as runningTotal
                from TestTable
                where somedate <= t.somedate
            ) as rt
order by t.somedate