Newbie SQL Query: Asking to fetch multiple entries in same table

Good Morning,

I'm new to SQL and although I'm getting better, I've got a query at the moment that is totally blinding me! It's probably really simple, and I was wondering if you could provide some help.

Basically, an application we use in my business records some information regarding a "Future Review Date" which would tell us when to contact the customer again.

I've written code that brings back all upcoming future review dates:

select xxxfolder.folderref, xxxperson.surname,xxxperson.forenames,xxxperson.nino, xxxperson.dob, fr.reviewdate, f.dateleft
from xxxfolder, xxxperson, xxxdeferment d, xxxfolderfuturereview fr,xxxfolderschemehist f
where xxxFOLDER.PERSONID = xxxPERSON.PERSONID
and xxxfolder.folderid = d.folderid
and xxxfolder.folderid = fr.folderid
and f.folderid=xxxfolder.folderid
and xxxfolder.folderstatusfg = 'D'

This brings up all the base data needed, I'm just having trouble adding one more line to the code that will only bring back records where there is more than one entry per customer on the review date screen.

A little help?

AE