Oracle MONTHS_BETWEEN

Why don't you just use MONTHS_BETWEEN Function? Doesn't that help?

SQL> SELECT sysdate FROM Dual;

SYSDATE
---------
01-JUN-09

SQL> SELECT MONTHS_BETWEEN (SYSDATE,
  2                         TO_DATE ('01/01/2009', 'DD/MM/YYYY')
  3                        ) diff_in_months
  4    FROM DUAL;

DIFF_IN_MONTHS
--------------
             5

SQL>