In Oracle the date difference is simply calculated as
difference of two date values. The query below can be
used to compute work load estimates in terms of week days,
manufacturing lead times, etc. The query shown below can
be joined with company or organizational calendar to
exclude holidays in work duration computation.
Note: When working with actual date values, TRUNC(start_date)
may be required to remove the time part in the date if time has
to be excluded.