[sql] WHERE Clause to find all records in a specific month

Can I just ask to compare based on the year and month?

You can. Here's a simple example using the AdventureWorks sample database...

DECLARE @Year       INT
DECLARE @Month      INT

SET @Year = 2002
SET @Month = 6

SELECT 
    [pch].* 
FROM 
    [Production].[ProductCostHistory]   pch
WHERE
    YEAR([pch].[ModifiedDate]) = @Year
AND MONTH([pch].[ModifiedDate]) = @Month