ถามเรื่องการเพิ่มข้อมูล 2 ตาราง เพิ่มข้อมูลไปแล้วไม่ยอมโชว์ในตาราง

private void ShowGrid()
        {
            string constr = Properties.Settings.Default.DatabaseCarserviceConnectionString;
            OleDbConnection conn = new OleDbConnection(constr);
            conn.Open();
            string sql = "SELECT [Bill].Bill_No ,[Bill].Bill_Date ,[Bill_Detail].Pro_ID ,[Product].Pro_Name_Model ,[Product].Price ,[Bill_Detail].Amount ,[Bill_Detail].Discount ,[Bill_Detail].Wage ,[Bill_Detail].S_Price ,[Bill].Car_ID From [Bill],[Bill_Detail],[Product] Where [Bill].Bill_No = [Bill_Detail].Bill_No AND [Bill_Detail].Pro_ID = [Product].Pro_ID = '" + txtBillNo.Text + "'";
            OleDbCommand cmd = new OleDbCommand(sql, conn);
            OleDbDataAdapter adapter = new OleDbDataAdapter(cmd);
            DatabaseCarserviceDataSet data = new DatabaseCarserviceDataSet();
            adapter.Fill(data, "[Bill_Detail]");
            gridControl1.DataSource = data.Tables["[Bill_Detail]"];
            conn.Close();
            gridView1.Columns[0].Caption = "BillNo";
            gridView1.Columns[1].Caption = "Date";
            gridView1.Columns[2].Caption = "ProID";
            gridView1.Columns[3].Caption = "ProName";
            gridView1.Columns[4].Caption = "Price";
            gridView1.Columns[5].Caption = "Amount";
            gridView1.Columns[6].Caption = "Discount";
            gridView1.Columns[7].Caption = "Wage";
            gridView1.Columns[8].Caption = "ToTal";
            gridView1.Columns[9].Caption = "CarID";
            btndel.Enabled = true;
        }

        private void btnadd_Click(object sender, EventArgs e)
        {
            string ConnStr = Properties.Settings.Default.DatabaseCarserviceConnectionString;
            OleDbConnection MyConn = new OleDbConnection(ConnStr);
            string insertSQL = "INSERT INTO [Bill] ([Bill_No],[Bill_Date],[Repair_Date],[ETC],[Car_ID],[Emp_ID]) values('" + txtBillNo.Text + "','"
                + txtDate.Text + "','" + txtRepair.Text + "','" + txtETC.Text + "','" + cmbCarID.Text + "','" + txtEmpID.Text + "')";
                OleDbCommand cmd = new OleDbCommand(insertSQL, MyConn);
                MyConn.Open();
                cmd.ExecuteNonQuery();
                MyConn.Close();

                string connStr = Properties.Settings.Default.DatabaseCarserviceConnectionString;
                OleDbConnection Conn = new OleDbConnection(connStr);
                string sql = "INSERT INTO Bill_Detail([Bill_No],[Pro_ID],[S_Price],[Discount],[Amount],[Wage]) values('" + txtBillNo.Text + "','"
                    + txtProID.Text + "','" + txtPrice.Text + "','" + txtDiscount.Text + "','" + txtAmount.Text + "','" + txtWage.Text + "')";
                    OleDbCommand Cmd = new OleDbCommand(sql, Conn);
                    Conn.Open();
                    Cmd.ExecuteNonQuery();
                    Conn.Close();

            ShowGrid();
        }