Changing a variable value within a query in SQL 2008 - sql

Question

If someone can help me with this, I will appreciate it.
I have 2 tables in sql 2008:
[users]
[userId] uniqueidentifier
[beginningDate] datetime
and [items]
[userId] uniqueidentifier
[itemDate] datetime
I want to count the number of users that have at least one item in [items] from January to December of any given year, I do this:
DECLARE #Year int = 2014, #Month int = 1 --January
SELECT ISNULL(Count(*), 0)
FROM [users]
WHERE
(
SELECT ISNULL(Count(*), 0) FROM [items]
WHERE [users].[userId] = [items].[userId]
AND YEAR([itemDate]) = #Year
AND ( MONTH([itemDate]) >= #Month AND MONTH([itemDate]) <= 12 )
) > 0
It works fine, the problem is that I want to check (and change accordingly), if the [beginningDate] is newer than #Month /#Year (it will always be the same year) then change the #Month variable to the [beginningDate] month value.

Answer 1

Thank to Allan S. Hansen for his reply.
I solved the problem by creating a function and calling it from my query:
CREATE FUNCTION [dbo].[GetMonth]
(
#UserId uniqueidentifier
, #Year int
)
RETURNS int
AS
BEGIN
DECLARE #Month int = 1; --January
DECLARE #DateValue DateTime
DECLARE #DateFrom DateTime = CONVERT(nvarchar(4), #Year) +'-03-01' --de mar
SELECT #DateValue =
CASE
WHEN [beginningDate] > #DateFrom THEN [beginningDate]
ELSE #DateFrom
END
FROM [users]
WHERE [userId] = #UserId
IF(#DateValue IS NULL)
SET #Month = 1;
ELSE
IF(#DateValue > #DateFrom) SET #Month = MONTH(#DateValue)
return #Month;
END
This is the new query:
DECLARE #Year int = 2014, #Month int = 1 --January
SELECT ISNULL(Count(*), 0)
FROM [users]
WHERE
(
SELECT ISNULL(Count(*), 0) FROM [items]
WHERE [users].[userId] = [items].[userId]
AND YEAR([itemDate]) = #Year
AND ( MONTH([itemDate]) >= [dbo].[GetMonth] ([users].[userId], #Year)
AND MONTH([itemDate]) <= 12 )
) > 0
Thanks anyway to all
Saludos
rubenc