หาเจอหล่ะ =.=!

Private Sub txtCustomerCode_BeforeUpdate(Cancel As Integer)

    Dim SID As String
    Dim stLinkCriteria As String
    Dim rsc As DAO.Recordset

    Set rsc = Me.RecordsetClone

    SID = Me.txtCustomerCode.Value
    stLinkCriteria = "[customer_code]=" & "'" & SID & "'"

    'Check customer table for duplicate customer code
    If DCount("customer_code", "customer", _
              stLinkCriteria) > 0 Then
        'Undo duplicate entry
        Me.Undo
        'Message box warning of duplication
        MsgBox "Warning Customer Code " _
             & SID & " has already been entered." _
             & vbCr & vbCr & "You will now been taken to the record.", _
               vbInformation, "Duplicate Information"
        'Go to record of original Customer Code
        rsc.FindFirst stLinkCriteria
        Me.Bookmark = rsc.Bookmark
    End If

    Set rsc = Nothing
End Sub