void Main()
{
    DataTable dt=new DataTable();  
    dt.Columns.Add("flightno");  
    dt.Columns.Add("flightTime",typeof(DateTime));  
    dt.Columns.Add("arrivalTime",typeof(DateTime));  
    dt.Columns.Add("passenger");  
    dt.Rows.Add("AU123",Convert.ToDateTime("2010-12-20 12:30"),Convert.ToDateTime("2010-12-20 15:30"),"小Q");  
    dt.Rows.Add("AU123",Convert.ToDateTime("2010-12-20 12:30"),Convert.ToDateTime("2010-12-20 15:30"),"小T");  
    dt.Rows.Add("AU123",Convert.ToDateTime("2010-10-21 12:00"),Convert.ToDateTime("2010-12-21 14:30"),"小N");  
    dt.Rows.Add("AU124",Convert.ToDateTime("2010-10-22 12:00"),Convert.ToDateTime("2010-12-22 11:30"),"小F");  
       
    var query=from t in dt.AsEnumerable()  
          group t by  new{t1=t.Field<DateTime>("flightTime"),t2=t.Field<DateTime>("arrivalTime")} into m  
          select new  
          {   
          flightTime=m.Key.t1,  
          arrivalTime=m.Key.t2  
          };  
          
   DataTable dtResult=new DataTable();
   dtResult.Columns.Add("flightTime",typeof(DateTime));  
   dtResult.Columns.Add("arrivalTime",typeof(DateTime));  
   query.ToList().ForEach(q=>dtResult.Rows.Add(q.flightTime,q.arrivalTime));
 
}