Valid If - for existing row

[HoScho]

I have a “valid if” condition whether a customer number exists. It works for a new entry but not when I edit the row. What can i do?

NOT(IN([KdNr] , kunden[KdNr]))

[Steve · Accepted solution]

NOT(
  IN(
    [KdNr],
    SELECT(
      kunden[KdNr],
      ([_ROWNUMBER] <> [_THISROW].[_ROWNUMBER])
    )
  )
)

[HoScho]

Thanks a lot!