Recursive calculation on CTE - sql-server-2012

Question

I'm looking for a way, how to calculate formula as below:
month 1
result_1 = result_0 + (number_of_open - number_of_close), where result_0 = 0
month 2
result_2 = result_1 + (number_of_open - number_of_close)
month 3
result_3 = result_2 + (number_of_open - number_of_close)
I know how to calculate it when results are shown from the very beginning, means:
but when I have some dates chosen, for example from February 1, 2015, it doesn't count correctly:
It seems to be counted from the taken moment.
Is there any idea how to solve it?

Answer 1

I found a good enough workaround for this. I've been searching how to solve this, and found that I can use SUM() OVER() and it will work as a Running Total. But if I need it to work inside given time-range, I had to use subquery, so I was not able to make it with CTE and had to use temp tables. My code is now:
IF OBJECT_ID('tempdb..#Temp1') IS NOT NULL BEGIN
drop table #Temp1
end
SELECT * into #Temp1
from (
SELECT
datepart(yy, t3.[datestamp]) AS full_year
,datepart(mm, t3.[datestamp]) AS month_number
,count(*) as number_of_activities
,t2.affected_item
FROM [sm70prod].[dbo].[ACTSVCMGTM1] AS t3
JOIN [sm70prod].[dbo].[INCIDENTSM1] AS t2 ON t3.number = t2.incident_id
WHERE
t2.affected_item like 'Service_name'
AND (t3.[type] LIKE 'Open')
GROUP BY t2.affected_item, datepart(yy, t3.[datestamp]), datepart(mm, t3.[datestamp])
)
as databases (full_year, month_number, number_of_activities, affected_item)
;
IF OBJECT_ID('tempdb..#Temp2') IS NOT NULL BEGIN
drop table #Temp2
end
SELECT * into #Temp2
from (
SELECT
datepart(yy, t3.[datestamp]) AS full_year
,datepart(mm, t3.[datestamp]) AS month_number
,count(*) as number_of_activities
,t2.affected_item
FROM [sm70prod].[dbo].[ACTSVCMGTM1] AS t3
JOIN [sm70prod].[dbo].[INCIDENTSM1] AS t2 ON t3.number = t2.incident_id
WHERE
t2.affected_item like 'Service_name'
AND (t3.[type] LIKE 'Closed')
GROUP BY t2.affected_item, datepart(yy, t3.[datestamp]), datepart(mm, t3.[datestamp])
)
as databases (full_year, month_number, number_of_activities, affected_item)
select * from (select sum(o.number_of_activities - c.number_of_activities) over (ORDER BY c.full_year, c.month_number) as [backlog]
from #Temp1 o full join #Temp2 c on o.full_year = c.full_year and o.month_number = c.month_number) sub
--where 'time condition'
and I can put my dates/time condition in 'where' clause.
Now the issue is how to correctly add it to the code where I use CTE and few 'selects' combined with 'union all's. But this is a story for another question, I guess.