SELECT  *

        FROM    ( SELECT    * ,

                            ROW_NUMBER() OVER ( PARTITION BY RIP_GUID ORDER BY RU_CreatedTime DESC ) rn

                  FROM      RIP_FlowInfo

                ) t

        WHERE   t.rn <= 1;

    var groupQuery = from t in query group t by t.RIP_Guid into g select new { key = g.Key, source = g.OrderByDescending(tt => tt.RU_CreatedTime).FirstOrDefault() };