Question

I have a Question table with the fields (QuestionID,QuestionMarks), and with the data fields look like –

 QuestionID   QuestionMarks
   1              1
   2              4
   5              1
   9              1
   12             2

which means at the moment Question table has 5 Question of Total 9 marks, Now my problem is that i want to know that a combination of 4 Questions with 8 marks is possible and fetch out that combination ( in general a combination of “x” questions of “y” marks is possible) ?

I was thinking to use CTE, but was afraid that it will take lot of time to execute the query if i have tens of thousand question.

please suggest some idea how to get the data. I am using SQL Server version 2008

Answer 1

This is a start. It’s going to have poor performance:

declare @Qs table (QuestionID int not null, QuestionMarks int not null)
insert into @Qs (QuestionID,QuestionMarks) values
(1,1), (2,4), (5,1), (9,1), (12,2)

declare @TargetMarks int = 8
declare @TargetCount int = 4

;with Build as (
    select QuestionID as MinID,QuestionID as MaxID,QuestionMarks as Total,1 as Cnt
        ,'/' + CONVERT(varchar(max),QuestionID) + '/' as QPath
    from @Qs
    union all
    select MinID,q.QuestionID,Total+q.QuestionMarks,Cnt+1,QPath + CONVERT(varchar(max),q.QuestionID) + '/'
    from
        Build b
            inner join
        @Qs q
            on
                b.MaxID < q.QuestionID and
                b.Total + q.QuestionMarks <= @TargetMarks and
                b.Cnt < @TargetCount
)
select * from Build where Cnt = @TargetCount and Total = @TargetMarks

Result set:

MinID       MaxID      Total       Cnt         QPath
--------------------------------------------------------------------------------
2           12          8           4           /2/5/9/12/
1           12          8           4           /1/2/9/12/
1           12          8           4           /1/2/5/12/

The tricky part is that the QPath value isn’t exactly the greatest way of storing ID values.