เอา Code ASP.Net มาฝาก DataTable(Excel) UNION DataTable(Database)

            string connectionString = "";
            if (FileUpload1.HasFile)
            {

                string fileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
                string fileExtension = Path.GetExtension(FileUpload1.PostedFile.FileName);
                string fileLocation = Server.MapPath("~/Files/" + fileName);
                FileUpload1.SaveAs(fileLocation);

                //Check whether file extension is xls or xslx

                if (fileExtension == ".xls")
                {
                    connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + fileLocation + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";
                }
                else if (fileExtension == ".xlsx")
                {
                    connectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + fileLocation + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=2\"";
                }

                //Create OleDB Connection and OleDb Command

                OleDbConnection con = new OleDbConnection(connectionString);
                OleDbCommand cmd = new OleDbCommand();
                cmd.CommandType = System.Data.CommandType.Text;
                cmd.Connection = con;

                OleDbDataAdapter dAdapter = new OleDbDataAdapter(cmd);
                DataTable dtExcelRecords = new DataTable();
                con.Open();

                DataTable dtExcelSheetName = con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                string getExcelSheetName = dtExcelSheetName.Rows[0]["Table_Name"].ToString();
                cmd.CommandText = "SELECT * FROM [" + getExcelSheetName + "]";
                dAdapter.SelectCommand = cmd;
                dAdapter.Fill(dtExcelRecords);
                con.Close();

                //connect DB
                string strconn = "select * from gen";
                SqlDataAdapter dtAdapter = new SqlDataAdapter(strconn, conn);
                tbGen = new DataTable();
                dtAdapter.Fill(tbGen);

                // ลบคอลั่ม ที่ไม่จำเป็นแล้วสร้างใหม่
                dtExcelRecords.Columns.RemoveAt(5);
                dtExcelRecords.Columns.Add("Next PM Date", typeof(String));


               //*********   วนลูป เพื่อเช็ค จาก Datatable(DB) *************//

                for (int i = 0; i < dtExcelRecords.Rows.Count; i++)
                {
                    dtExcelRecords.Rows[i][5] = string.Empty;

                    DataRow[] rows = tbGen.Select("[Location] = '" + dtExcelRecords.Rows[i][0].ToString() + "' and [Customer_Agreement] = '" + dtExcelRecords.Rows[i][2].ToString() + "' ");


                    if (rows.Length > 0)
                    {
                        foreach (DataRow r in rows)
                        {
                            dtExcelRecords.Rows[i][5] = r["new_date"].ToString();
                        }
                    }
                }



                
               GridView1.DataSource = dtExcelRecords;
               GridView1.DataBind();