private void Return_Product_Form_Load(object sender, EventArgs e) { label_return.Hide(); textBox_product_name.Hide(); Ok_button_Product_name.Hide(); conn = new OracleConnection(ordb); conn.Open(); OracleCommand cmd = new OracleCommand(); cmd.Connection = conn; cmd.CommandText = "select Bill_id from Bill"; cmd.CommandType = CommandType.Text; OracleDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { Select_Bill_ID_for_return_bill.Items.Add(dr[0]); } dr.Close(); }