ให้เลขที่ใบเสร็จ +ค่าไปเรื่อยๆคะ BO1 พอถึง BO10 แล้วมันไม่บวกค่าเพิ่ม คะ รบกวนทีคะ

                SQLStatement1 = "SELECT *   FROM product_or_detail order by MID(bill_id,3,6) desc"
                'SQLStatement1 = "select * from product_or_detail order by bill_id desc "
                cmd2 = New MySqlCommand(SQLStatement1, SQLConnection)
                Dim a As MySqlDataReader = cmd2.ExecuteReader

                a.Read()
                If a.HasRows Then
                    count = a("bill_id")
                    Dim billid_sum As Integer
                    Dim b As String
                    b = count
                    txtbillid.Text = b.Substring(2)
                    billid_sum = Convert.ToInt32(txtbillid.Text)
                    billid_sum = billid_sum + 1
                    txtbillid.Text = "BO" + Convert.ToString(billid_sum)

                Else
                    txtbillid.Text = "BO1"
                End If