limit the number of months in ssrs - sql-server

Question

I have a dataset, output of a sql query which gives me the below output :
Year Month TotalSales TotalProducts
2013 1 23233 45
2013 2 3344 43
2013 3 232 11
2013 4 2232 23
I am trying to represent the above dataset in a table and a bar graph using SSRS.
Is there a way I can limit the months to the last three months on SSRS ??
I am using the current month as a parameter in SSRS.
So example : I choose month 4 as a parameter , i would like to see the results only for the months 4,3 & 2 in the bar chart and the table
Is there a way I can do it ?
The actual query looks something like this :
SELECT ISNULL(x.[Month],z.[Month]) AS [Month],
ISNULL(x.Sum_Stores, 0) - ISNULL(y.Sum_SalesStores, 0) AS Difference , ISNULL(Sum_onetonine, 0) as EcontractsbetweenOneandNine........................
FROM
(
SELECT [Month], Sum(Stores) AS Sum_Stores
FROM SUM_XXX
WHERE [Year] = '2013' and Name = 'Pro'
GROUP BY [Month]
) AS x
FULL OUTER JOIN
(
SELECT [Month], Sum(tracts) AS Sum_SalesStores
FROM SUM_yyy
WHERE [Year] = '2013' and Name = 'Pro'
GROUP BY [Month]
) AS y ON x.[Month] = y.[Month]
............................

Answer 1

declare #ParamDate DateTime =null; -- Pass the required date in datetime format
-- as per your example pass #ParamDate as '20130401'
SET #ParamDate = getdate(); --setting the current date for demo purpose
SELECT ISNULL(x.[Month],z.[Month]) AS [Month],
ISNULL(x.Sum_Stores, 0) - ISNULL(y.Sum_SalesStores, 0) AS Difference , ISNULL(Sum_onetonine, 0) as EcontractsbetweenOneandNine........................
FROM
(
SELECT [Month], Sum(Stores) AS Sum_Stores
FROM SUM_XXX
WHERE ([Year] = year(#ParamDate) or [Year] = year(dateadd(m,-2,#ParamDate)) )
and ([Month] = month(#ParamDate) or [Month] = month(dateadd(m,-2,#ParamDate)) )
and Name = 'Pro'
GROUP BY [Month]
) AS x
FULL OUTER JOIN
(
SELECT [Month], Sum(tracts) AS Sum_SalesStores
FROM SUM_yyy
WHERE ([Year] = year(#ParamDate) or [Year] = year(dateadd(m,-2,#ParamDate)) )
and ([Month] = month(#ParamDate) or [Month] = month(dateadd(m,-2,#ParamDate)) )
and Name = 'Pro'
GROUP BY [Month]
) AS y ON x.[Month] = y.[Month]
............................

Answer 2

There are several ways to achieve this in SSRS.
Do you want to limit the results returned by the query if so use a query parameter link
Or you can apply a filter to the dataset / dataregion link
What you will essentially want to do would be (pseudo)
DataSet!Month.Value BETWEEN Parameter!Month.Value-2 AND Parameter!Month.Value
That doesn't take into considertion months 1 and 2 properly. Will update when I have a better solution then a convoluted if-else.
Edit: If you added a MonthStart field to the result set as a proper DATETIME and used MonthStart as values to the parameter then you could do
DataSet!Month.Value BETWEEN DATEADD (MONTH, -2, Parameter!Month.Value) AND Parameter!Month.Value