Question

I’ve the following table (both A and B are integers):

Update 1 – Could anyone do me a favour and run the solution on a set of 1M records with B being a random decimal (to avoid overflows) residing in [0 to 1] range for N=> 10, 100 and 1000? I’d like to get a flavor of the time, required to run the solution query. Thanks a lot in advance.

Sample data:

A   B
1   1
2   8
3   1
4   11
5   1
6   1
7   6
8   1
9   1
10  2

How do I get the maximum Sum of B values for any N sequential A‘s? The solution mustn’t use cursors, usage of table vars/tem tables has to be stongly justified.

I can use SQLCLR in case if it’ll give a distinct performance boost.

Some clarifications:

• Max Sum for 1 element is 11 (see A = 4)
• Max Sum for 2 elements is 12 (it’s either A=> 1 & 2 or A=> 2 & 3),
• Max Sum for 3 elements is 20 (A=>2, 3, 4),
• Max Sum for 4 is 21 (A=>1,2,3,4 or A=>2,3,4,5) etc.

Answer 1

Since the A values are guaranteed to be consecutive integers, given N we know for any particular A which values we are interested in. So

SELECT
    A,
    (SELECT SUM(B) FROM Table T2 WHERE T.A <= T2.A AND T2.A <= T.A + N - 1) 
        AS SumOfBs
FROM Table T
WHERE A + N - 1 <= (SELECT COUNT(*) FROM Table)

gives, for each A, the sum of the B values for the N rows starting there. The WHERE restricts us to rows that do actually have N rows starting there. Put this in a subquery and we can get the maximum:

SELECT 
    MAX(SumOfBs) AS DesiredValue
FROM
(
    SELECT
        A,
        (SELECT SUM(B) FROM Table T2 WHERE T.A <= T2.A AND T2.A <= T.A + N - 1) 
            AS SumOfBs
    FROM Table T
    WHERE A + N - 1 <= (SELECT COUNT(*) FROM Table)
) Intermediate

should do the job.