The following query finishes in 2 seconds:

SELECT *
FROM Response 
WHERE BatchID=2
AND Response=1 AND Amount>=500

Next query also finishes in about 2 seconds:

SELECT * 
FROM Response 
WHERE BatchID=2 AND Listcode NOT IN (SELECT CASE WHEN nListcode='' THEN oListcode ELSE nListcode END FROM RawData WHERE CampaignID=@CampaignID AND Mailed>0 GROUP BY CASE WHEN nListcode='' THEN oListcode ELSE nListcode END)

However, following combination of the first two WHERE condition takes almost 3 minutes to complete.

SELECT *
FROM Response 
WHERE BatchID=2
AND Response=1 AND Amount>=500
AND Listcode NOT IN (SELECT CASE WHEN nListcode='' THEN oListcode ELSE nListcode END FROM RawData WHERE CampaignID=@CampaignID AND Mailed>0 GROUP BY CASE WHEN nListcode='' THEN oListcode ELSE nListcode END)

Can anyone tell me why and how to optimize this last query? TIA.