How to compare two date and to find out whether the date difference is within 3 months in SQL Server? Does anyone know how to compare two date and to find out whether the date difference is within 3 months in SQL Server?
Example if I have 2 dates:
Start_Date = '2013-02-01'
End_Date = '2013-04-10'

How can I compare two date and to find out whether the date difference is within 3 months in SQL Server?

Look into using DATEDIFF:
SELECT *
FROM YourTable
WHERE DATEDIFF(month, start_date, end_date) <= 3

SQL Fiddle Demo
MSDN: http://msdn.microsoft.com/en-us/library/ms189794.aspx

Here's the answer using the two dates you provided in your question.  I gave it to you two ways.  The first column is the comparison of whether it is within 3 months.  The second column is simply the result of the SQL Server system function DATEDIFF.
DECLARE @Start_Date DATE = '2013-02-01',
@End_Date   DATE = '2013-04-10'

SELECT CASE
WHEN datediff(MONTH, @Start_Date, @End_Date) <= 3 THEN
'True'
ELSE
'False'
       END AS [WithinThreeMonths]
     , datediff(MONTH, @Start_Date, @End_Date) [Months]