SELECT
*
FROM (
SELECT
     groupId
    ,agentId
    ,CASE WHEN ISNUMERIC(RIGHT(impPackageCode, 4)) = 1 THEN CONVERT(INT, RIGHT(impPackageCode, 4)) ELSE NULL END as [Year]
FROM
    att_schema.att_nmfData
WHERE agentId IS NOT NULL
    AND CASE WHEN ISNUMERIC(RIGHT(impPackageCode, 4)) = 1 THEN CONVERT(INT, RIGHT(impPackageCode, 4)) ELSE 2009 END IN ( 2011, 2010 )
) x WHERE [Year] = '2011'