How to query data in the same table

[#1]

I want to query data in the same table.

Date	Product
20-JUL-13	REP
30-JUL-13	REV
15-DEC-13	REP
12-DEC-13	REV
13-DEC-13	REV

My expected algorithm is:

1. Match all REP with REV and date < 30 days from today and mark that as 'MATCH'

2. Match all REP with REV and date > 30 days from today and mark that as 'UNMATCH'

How can I do this in QV?