SELECT co1.VideoId, co1.UserName, co1.DateViewed, co1.VideoTitle
  FROM cs_VideoViewTracking AS co1,
       (SELECT ItemId, MAX(DateViewed) AS maxview
          FROM cs_VideoViewTracking
        GROUP BY ItemID ) AS co2
  WHERE co2.ItemId = co1.ItemId
        and co1.DateViewed = co2.maxview