How to get cumulative sum

Question

declare  @t table
    (
        id int,
        SomeNumt int
    )

insert into @t
select 1,10
union
select 2,12
union
select 3,3
union
select 4,15
union
select 5,23         


        

Answer 1

Above (Pre-SQL12) we see examples like this:-

SELECT
    T1.id, SUM(T2.id) AS CumSum
FROM 
    #TMP T1
    JOIN #TMP T2 ON T2.id < = T1.id
GROUP BY
    T1.id

More efficient...

SELECT
    T1.id, SUM(T2.id) + T1.id AS CumSum
FROM 
    #TMP T1
    JOIN #TMP T2 ON T2.id < T1.id
GROUP BY
    T1.id