How do I prevent entering multiple records?

[Guest]

I have a fairly simple database with 1000 records (names and addresses) with
two "one to many" linked tables. What I would like to have happen is when a
last name is entered that is already in the database it brings up a list of
those records so it can be determined whether or not it is a duplicate.
I have tried creating a multiple field index but I can't save my table
because it says it creates duplicate records (is this because I already have
dupes in the data?)

 

[Allen Browne]

Use the BeforeUpdate event of the form to OpenForm to show a list of the
matghing names, and determine if this is a duplicate.

If so, cancel the form's BeforeUpdate event, and undo the form.

This kind of optional warning cannot be done without a form.