How do I count the occurrence of a value in a column of type 2 slowly changing dimension?

Question

I have my question altered as is viewed as vague. I have a table as below:

Id    AltId    DateFrom    DateTo     CurrentFlag    Value
1     23       2015-04-01  2015-05-31 0              0
2     23       2015-05-31  Null       1              50
3     45       2015-06-01  Null       1              0
4     60       2015-07-01  Null       1              0

I want to achieve a count where Value is 0 for the past six months. Expected results:

Month    Count

4        1
5        1
6        1
7        2
8        2
9        2

This is supposed to be cumulative count but the AltId ceases in a month where it changes value to anything greater than 0 like is the case with AltId 23. Cumulative count is not an issue but how to not include an AltId when it's value changes from 0.

I'm not sure if this makes sense this time around. I'm using Sql Server 2008.

I'm wondering why this script doesn't do what I expect:

declare @a table
(   
    id int
    ,altId int
    ,startDate date
    ,endDate date
    ,currentFlag bit
    ,value int
)

insert into @a
values
    (1,23,'2015-04-01','2015-05-31',0,0)
    ,(2,23,'2015-05-31',null,1,50)
    ,(3,45,'2015-06-01',null,1,0)
    ,(4,60,'2015-07-01',null,1,0)

declare @s date =DATEADD(m, -5, convert(date, convert(varchar(6), getdate(),112) + '01')), @e date = getdate();

;with d([Month],DateKey) as
(
    select month(@s) [Month],@s DateKey
        union all
    select  
        month(DateKey),dateadd(day,1,DateKey) 
    from 
        d
     where d.DateKey>= @s and d.DateKey<=@e
) 
select 
       d.Month
       ,count(distinct a.altId) as 'Count'
from 
       d
              left join
       @a a
on
       d.dateKey between a.startDate and isnull(a.endDate,getdate())
              and
       a.value=0
group by
       d.[Month]

option (maxrecursion 186)

Any idea?

Answer 1

This does the trick.

declare @a table
    (   
        id int
        ,altId int
        ,startDate date
        ,endDate date
        ,currentFlag bit
        ,value int
    )

    insert into @a
    values
        (1,23,'2015-04-01','2015-05-31',0,0)
        ,(2,23,'2015-05-31',null,1,50)
        ,(3,45,'2015-06-01',null,1,0)
        ,(4,60,'2015-07-01',null,1,0)

    declare @s date =DATEADD(m, -5, convert(date, convert(varchar(6), getdate(),112) + '01')), @e date = getdate();
    select @s,@e
    ;with d([Month],DateKey) as
    (
        select month(@s) [Month],@s DateKey
            union all
        select  
            month(dateadd(day,1,DateKey)),dateadd(day,1,DateKey) 
        from 
            d
         where d.DateKey>= @s and dateadd(day,1,DateKey)<=@e
    ) 
    select 
           d.Month
           ,count(distinct a.altId) as 'Count'
    from 
           d
                  left join
           @a a
    on
           d.dateKey between a.startDate and isnull(a.endDate,getdate())
                  and
           a.value=0
    group by
           d.[Month]

    option (maxrecursion 186)