Code Gen ID จากค่ามากที่สุด ใน Database [Code VB.net]

        Dim a As String = "00"

        Dim sql As String = "Select max(UnitID)  from Unit "
        command = New SqlCommand
        command.CommandText = sql
        command.CommandType = CommandType.Text
        command.Connection = conn
        command.ExecuteNonQuery()

        da = New SqlDataAdapter(command)
        ds = New DataSet

        da.Fill(ds, "Unit")

        Dim g As String = ds.Tables("Unit").Rows.ToString.Substring(0, 2)

        Dim num As Integer = Int32.Parse(g)
        num += 1
        Dim b As String = num.ToString()
        Dim c As String = b.Length.ToString()
        Dim d As String = a.Substring(Int32.Parse(c))

        '  txtID.Text = d + num
     
        MsgBox(d + num)