How to prevent duplicate entries - combination of 3 fields

[InDFW]

I am trying to prevent duplicate entries, but the record is only duplicate if 3 fields are identical between records.

For example:
CC# (unique)
Number (*)
Title
FromRev (*)
ToRev (*)
Changes
Void

If [Number], [FromRev], and [ToRev] match another record, the user should not be allowed to go any further.

I need help with the If statement and also suggestions on what should happen when a duplicate record is entered.

I am thinking I want a pop-up to notify of duplicate entry, the record to automatically void (I have a void check box), and subsequent entries need to begin a new record. (Open to suggestions here)

I should probably note (warn) I am not code-savvy, but have used it before. If this needs code, I might be very needy...

 

[MStef]

Look at "Demo3fieldsIndexA2000.mdb" (attachment, zip).
There you have got 2 fields.
A "Demo3fieldsIndexA2000.mdb", open form1 and try to enter the sema record.
An "Index3fields" word, about Index on 3 fields, in your table.

 

[InDFW]

Thank you so much!
I have to find and delete/void the duplicate entries before it will let me save, but looks like this is exactly what I needed.