Hoe to put If Else condition to check one coulmn value is present in another set of column values in sql 2008

Hi All,

I have main data set which consists of lacks of records and below is my query

DECLARE @USER_DT DATETIME 
SET @USER_DT = '2013-08-01'
DECLARE @RANGE_DATE DATETIME
SELECT distinct @RANGE_DATE = RANGE_DATE 
FROM
  dbo.TABLE 
WHERE
  RANGE_DATE >= (CONVERT(VARCHAR(8), DATEADD (M, -2, GETDATE()), 21)+ '26')
  AND
  RANGE_DATE <= (CONVERT(VARCHAR(8), DATEADD (M, -1, GETDATE()), 21)+ '25')
IF(@USER_DT = @RANGE_DATE )			
BEGIN
SELECT	* 
FROM	MAIN_TABLE
WHERE	
		USER_DATE = @USER_DT
		AND
		RANGE_DATE >= (CONVERT(VARCHAR(8), DATEADD (M, -2, GETDATE()), 21)+ '26') 
		AND
		RANGE_DATE <= (CONVERT(VARCHAR(8), DATEADD (M, -1, GETDATE()), 21)+ '25')
END
BEGIN
SELECT	* 
FROM	MAIN_TABLE
WHERE	
		USER_DATE = @USER_DT
		AND
		RANGE_DATE >= (CONVERT(VARCHAR(8), DATEADD (M, -1, GETDATE()), 21)+ '26') 
		AND
		RANGE_DATE <= (CONVERT(VARCHAR(8), DATEADD (M, 0, GETDATE()), 21)+ '25')
END

i.e. @USER_DT is for user selection in SSRS Report window. Now, let say he has enter '2013-08-01' now second parameter @RANGE_DT is created for storing distinct dates values now my problem is I  want to check that user entered date in @Range_DT and if it is present as shown in the above query i will get desired output. But thing is we can check only single value in If-Else and I wanna check single date value is present or not and displya output accordingly. Is there any way to do this (This later i am going to put in SSRS report).