SQL Server：按列总和分组

Question

I need to aggregate data by one column which contains numeric data.

I have data like:

ID | Amount
---+-------
1  | 44
2  | 15
3  | 16
4  | 8
5  | 16 

Result, which I expect is:

ID | Amount
---+-------
1  | 44
2  | 31
4  | 24

Query should group data ordered by ID column by Amount column in parts of max sum of amount 32. If amount is greater then 32 then it should be presented as one 'group'. Result should contain Min(ID) and SUM(Amount) which can't be greater than 32 when group more than one record.

Answer 1

The only way that I know how to accomplish this is using iteration (although in your case if you have enough single values over 32, then you might be able to use a more efficient approach).

Iteration in SQL Server queries is handled by recursive CTEs (once you forswear cursors):

with v as (
      select *
      from (values (1, 44), (2, 15), (3, 16), (4, 8), (5, 16) ) v(id, amount)
     ),
     t as (
      select v.*, row_number() over (order by id) as seqnum
     ),
     cte as (
      select seqnum, id, amount, id as grp
      from t
      where seqnum = 1
      union all
      select t.seqnum, t.id,
             (case when t.amount + cte.amount > 32 then t.amount else t.amount + cte.amount end) as amount,
             (case when t.amount + cte.amount > 32 then t.id else cte.grp end) as grp
      from cte join
           t
           on cte.seqnum = t.seqnum + 1
     )
select grp, max(amount)
from cte
group by grp;

I should note that the use of max(amount) in the outer query assumes that the values are never negative. A slight modification can handle that situation.

Also, the intermediate result using t is not strictly necessary for the data you have provided. It ensures that the columns used in the join actually have no gaps.

Answer 2

You can try this version with rownumbers assigned initially and each row is joined to the previous one in a recursive cte. And if the running sum > 32 a new group starts.

with rownums as (select t.*,row_number() over(order by id) as rnum from t)
,cte(rnum,id,amount,runningsum,grp) as (select rnum,id,amount,amount,1  from rownums where rnum=1
                                        union all
                                        select t.rnum,t.id,t.amount
                                        ,case when c.runningsum+t.amount > 32 then t.amount else c.runningsum+t.amount end
                                        ,case when c.runningsum+t.amount > 32 then t.id else c.grp end
                                        from cte c
                                        join rownums t on t.rnum=c.rnum+1
                                      )
select grp as id,max(runningsum) as amount
from cte
group by grp

Sample Demo