请教：关于自动编号--前缀(变量)+顺序号

Private Sub dtjm_AfterUpdate()
    Dim maxno As String
    Dim i As Long
    Me.Refresh
    maxno = Nz(DMax("[dtzh]", "tbltzmx_s", "left([dtzh],(len([dtzh])-3))='" & Me.dtjm & "'"), 0)    '找到最后记录的编号
    If maxno = "0" Then
        Me.dtzh = Me.dtjm & "001"
    Else
        i = Val(Right(maxno, 3)) + 1
        Me.dtzh = Left(maxno, Len(maxno) - 3) & Format(i, "000")
    End If
End Sub