select CONCAT(client,campaign),id FROM cmdata
WHERE id IN (SELECT id FROM cmdata GROUP BY campaign HAVING COUNT(*) > 1)
Or also very effective , this will work if both the fields are the same…..(like a concat)
delete from cmdata
USING cmdata, cmdata as vtable
WHERE (cmdata.id > vtable.id)
AND (cmdata.campaign=vtable.campaign)
AND (cmdata.client=vtable.client)
