I'm not sure if I understand correctly. I created a recordset that I filtered (right Join !?) that shows cardnumberID from both columns:
Here is the recordset:
SELECT Giftcard.GiftcardID, Booking.BookingGiftcardnoID
FROM Giftcard RIGHT OUTER JOIN Booking ON Giftcard.GiftcardID = Booking.BookingGiftcardnoID
Then, how do I compare / validate when the form field is filled in?