Help redoing a query resulting in many unions

Question

Trying to do a query that basically shows a when a customer was visited in a certain period.
I have done this as follows:
SELECT custname,
  sysdate dateperiodfor,
  MAX(datevisited)datevisited
FROM visited,customer
WHERE custid          =visitedcustid
AND datevisited        < sysdate
GROUP BY custname, sysdate
UNION
SELECT custname,
  add_months(sysdate,-1)dateperiodfor,
  MAX(datevisited)datevisited
FROM visited,customer
WHERE custid          =visitedcustid
AND datevisited        < sysdate
GROUP BY custname,  add_months(sysdate,-1)Which works fine apart from however many months i want the dateperiodfor to go back i need to add another union and change the ADD_MONTHS(sysdate) -1 to -2, -3 etc.
Is there a better way i can structure so I can go back a set number of months i.e. 12 or 18 without the need for 12 or 18 unions?
Its going to be a VIEW though so may need to be hard coded number?

Answer 1

Dynamic SQL is probably not needed in this scenario. However, when you have questions like this it's always helpful to
1. Oracle version (SELECT * FROM V$VERSION)
2. Sample data in the form of CREATE / INSERT statements.
3. Expected output
4. Explanation of expected output (A.K.A. "business logic")
5. Use \ tags for #2 and #3. See FAQ (Link on top right side) for details.
Also see the third post in this thread:
{thread:id=2174552}