I am new to this place as well, but recenly was working with dates. So here is my solution.
You coud add extra condition for WHERE. Like this?
AND c.END_DATE is between March 2009 and July 2009
Example use of between:
WHERE order_date between to_date ('2003/01/01', 'yyyy/mm/dd')
AND to_date ('2003/12/31', 'yyyy/mm/dd');