Problem in update

Question

try
  {
  OleDbConnection con = new OleDbConnection(ConnectionString);
  con.Open();
  string s1 = dtp_date.Value.ToShortDateString();
  OleDbCommand cmd = new OleDbCommand("update dbo_Diesel_Master set Petrol_pump_name='" + txt_Petrl_pump_name.Text + "',Vehicle_No='" + cmb_VehicleNo.Text + "',Fuel='" + txt_Fuel.Text + "',Rate='" + txt_rate.Text + "',Date='" + s1 + "',Challan_No='" + txt_challan_no.Text + "',Amount='" + txt_amt.Text + "' where Petrol_pump_name='" + DGV_Diesel.SelectedRows[0].Cells[0].Value + "'", con);
  cmd.ExecuteNonQuery();
  cmd = new OleDbCommand("select * from dbo_Diesel_Master", con);
  dr = cmd.ExecuteReader();
  DataTable dt = new DataTable();
  dt.Load(dr);
  DGV_Diesel.DataSource = dt;
  MessageBox.Show("updated successfully.....");
  con.Close();
  }
  catch (Exception ex)
  {
  MessageBox.Show("please select a record for delete..");
  }