insrt querry problem

On an initial look, I noticed that you are closing connection on each loop iteration. You need to close the connection once you finished all your insertion (i.e. outside of the loop)

{ string query = "select t2.date,t1.FlightNo,t1.Dept_Time,t1.Arr_Time,t1.Route,t1.[Destination 1],t1.[Destination 2],t1.[Destination 3],t1.[Destination 4] From [FlightNumber] t1 inner join [schedule] t2 on t1.FlightNo=t2.FlightNo"; OleDbCommand cmd = new OleDbCommand(query, con); OleDbDataAdapter adp = new OleDbDataAdapter(cmd); dt1 = new DataTable(); adp.Fill(dt1); con.Open(); // (date,[Flight_no],[Dept_time],[Arr_time],Route,[dest_1],dest2,dest3,dest4)values string query2 = "insert into days ([date],Flight_no,Dept_time,Arr_time,Route,dest_1,dest2,dest3,dest4)values(@date,flight_no,@dept_time,@arr,@route,@dest,@dest2,@dest3,@dest4)"; for (int i = 0; i < dt1.Rows.Count; i++) { OleDbCommand cmd1 = new OleDbCommand(query2, con); cmd.Parameters.AddWithValue("@date" ,SqlDbType.NVarChar).Value = dt1.Rows[i]["date"].ToString(); cmd.Parameters.AddWithValue("@flight_no", dt1.Rows[i]["FlightNo"]); cmd.Parameters.AddWithValue("@dept_time", dt1.Rows[i]["Dept_Time"]); cmd.Parameters.AddWithValue("@arr", dt1.Rows[i]["Arr_Time"]); cmd.Parameters.AddWithValue("@route", dt1.Rows[i]["Route"]); cmd.Parameters.AddWithValue("@dest_1", dt1.Rows[i]["Destination 1"]); cmd.Parameters.AddWithValue("@dest2", dt1.Rows[i]["Destination 2"]); cmd.Parameters.AddWithValue("@dest3", dt1.Rows[i]["Destination 3"]); cmd.Parameters.AddWithValue("@dest4", dt1.Rows[i]["Destination 4"]); cmd1.ExecuteNonQuery(); con.Close(); MessageBox.Show("successfully inserted"); } } private void datetime_Leave_1(object sender, EventArgs e) { txtday.Text = this.datetime.Value.DayOfWeek.ToString(); }

Could you please paste your SQL query here... I generally avoid to download stuff from forums.