-- Overlap present

select 'YES' as overlap from dual
    where          (date '2007-01-01', date '2008-01-01')
          overlaps (date '2005-01-01', date '2009-01-01')


OVE
---
YES

-- Overlap not present

select 'YES' as overlap from dual
    where          (date '2007-01-01', date '2008-01-01')
          overlaps (date '2005-01-01', date '2006-01-01')


no rows selected.

http://oraclesponge.wordpress.com/2008/06/12/the-overlaps-predicate/

This function can be used to find out if there exists an overlap between two pairs of dates or time.

There is an alternate way to calculate the actual overlapping value - Read the snippet "How to avoid double counts"

Oracle - Overlaps function

sql, Oracle

SQL