Finding duplicates using 3 fields where a 4th field makes it unique

[Mike Bollinger]

Using Infomaker 8 on an Oracle Database:

I have data with forename, surname and DOB. I can find duplicates in
these
three fields using the following SQL:

Select person.forename, person.surname, person.dob from person
group by person.forename, person.surname, person.dob
having count(*)>1

When you include a 4th field, external_person_reference, all the above
records return unique.

I am trying to retrieve a list of these forename, surname, DOB that
are duplicate and Ext_ref that distinguishes them.

eg.
Dave Bennett 25/12/1960 REF1234
Dave Bennett 25/12/1960 LIV9923

Can someone suggest a way this can be done in Infomaker?

Thanks,
Mike