How to get cumulative sum

Question

select t1.id, t1.SomeNumt, SUM(t2.SomeNumt) as sum
from @t t1
inner join @t t2 on t1.id >= t2.id
group by t1.id, t1.SomeNumt
order by t1.id

SQL Fiddle example

Output

| ID | SOMENUMT | SUM |
-----------------------
|  1 |       10 |  10 |
|  2 |       12 |  22 |
|  3 |        3 |  25 |
|  4 |       15 |  40 |
|  5 |       23 |  63 |

Edit: this is a generalized solution that will work across most db platforms. When there is a better solution available for your specific platform (e.g., gareth's), use it!

The latest version of SQL Server (2012) permits the following.

SELECT 
    RowID, 
    Col1,
    SUM(Col1) OVER(ORDER BY RowId ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS Col2
FROM tablehh
ORDER BY RowId

or

SELECT 
    GroupID, 
    RowID, 
    Col1,
    SUM(Col1) OVER(PARTITION BY GroupID ORDER BY RowId ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS Col2
FROM tablehh
ORDER BY RowId

This is even faster. Partitioned version completes in 34 seconds over 5 million rows for me.

Thanks to Peso, who commented on the SQL Team thread referred to in another answer.

For SQL Server 2012 onwards it could be easy:

SELECT id, SomeNumt, sum(SomeNumt) OVER (ORDER BY id) as CumSrome FROM @t

because ORDER BY clause for SUM by default means RANGE UNBOUNDED PRECEDING AND CURRENT ROW for window frame ("General Remarks" at https://msdn.microsoft.com/en-us/library/ms189461.aspx)

Let's first create a table with dummy data:

Create Table CUMULATIVESUM (id tinyint , SomeValue tinyint)

Now let's insert some data into the table;

Insert Into CUMULATIVESUM
    Select 1, 10 union 
    Select 2, 2  union
    Select 3, 6  union
    Select 4, 10 

Here I am joining same table (self joining)

Select c1.ID, c1.SomeValue, c2.SomeValue
From CumulativeSum c1, CumulativeSum c2
Where c1.id >= c2.ID
Order By c1.id Asc

Result:

ID  SomeValue   SomeValue
-------------------------
1   10          10
2   2           10
2   2            2
3   6           10
3   6            2
3   6            6
4   10          10
4   10           2
4   10           6
4   10          10

Here we go now just sum the Somevalue of t2 and we`ll get the answer:

Select c1.ID, c1.SomeValue, Sum(c2.SomeValue) CumulativeSumValue
From CumulativeSum c1,  CumulativeSum c2
Where c1.id >= c2.ID
Group By c1.ID, c1.SomeValue
Order By c1.id Asc

For SQL Server 2012 and above (much better performance):

Select 
    c1.ID, c1.SomeValue, 
    Sum (SomeValue) Over (Order By c1.ID )
From CumulativeSum c1
Order By c1.id Asc

Desired result:

ID  SomeValue   CumlativeSumValue
---------------------------------
1   10          10
2   2           12
3   6           18
4   10          28

Drop Table CumulativeSum

A CTE version, just for fun:

;
WITH  abcd
        AS ( SELECT id
                   ,SomeNumt
                   ,SomeNumt AS MySum
             FROM   @t
             WHERE  id = 1
             UNION ALL
             SELECT t.id
                   ,t.SomeNumt
                   ,t.SomeNumt + a.MySum AS MySum
             FROM   @t AS t
                    JOIN abcd AS a ON a.id = t.id - 1
           )
  SELECT  *  FROM    abcd
OPTION  ( MAXRECURSION 1000 ) -- limit recursion here, or 0 for no limit.

Returns:

id          SomeNumt    MySum
----------- ----------- -----------
1           10          10
2           12          22
3           3           25
4           15          40
5           23          63