用LINQ( group by having) 找出Datatable中的重复数据

private void butCF_Click(object sender, RoutedEventArgs e)
        {
            if (DatagridDatatable != null && DatagridDatatable.Rows.Count > 0)
            {
//group by 日期,合同号,部门 having count(记录编号)>0    找出 日期 合同号 部门重复的记录
                var query = (from t in DatagridDatatable.AsEnumerable()
                            group t by new { t1 = t.Field<DateTime>("日期"), t2 = t.Field<Int64>("合同号"), t3 = t.Field<string>("部门") } into                            m
                            select new
                            {
                                日期 = m.Key.t1,
                                合同号 = m.Key.t2,
                                部门 = m.Key.t3,
                                记录编号=m.First().Field<Decimal>("记录编号"),//这里要写这句话，否则查不出query
                                rowcount = m.Count()
                            } into c where c.rowcount>1 select c).ToList();

                DataTable dt = new DataTable();
                ////dt.Columns.Add("序号",System.Type.GetType( "System.Int32"));
                dt.Columns.Add("日期", System.Type.GetType("System.DateTime"));
                dt.Columns.Add("合同号", System.Type.GetType("System.Int64"));
                dt.Columns.Add("部门", System.Type.GetType("System.String"));
                dt.Columns.Add("记录编号", System.Type.GetType("System.Decimal"));
                dt.Columns.Add("销售金额", System.Type.GetType("System.Decimal"));
                foreach (var q in query)
                {
                    DataRow[] dr_finds = DatagridDatatable.Select("日期='" + q.日期 + "' and 合同号=" + q.合同号 + " and 部门='" + q.部门+"'");
                    foreach (DataRow find in dr_finds)
                    {
                        DataRow dr = dt.NewRow();
                        dr["日期"] = find["日期"];
                        dr["合同号"] = find["合同号"];
                        dr["部门"] = find["部门"];
                        dr["记录编号"] = find["记录编号"];
                        dr["销售金额"] = find["销售金额"];
                        dt.Rows.Add(dr);
                    }
                }
                if (dt.Rows.Count > 0)
                {
                   fmCFJL win=new  fmCFJL(dt);
                   win.Show();
                }
                else
                {
                    MessageBox.Show("没有重复记录");
                    return;
                }
            }
        }