MONTHS_BETWEEN function
MONTHS_BETWEEN(x,y) returns the number of months between x and y.
If x is before y on the calendar, the number returned is positive;
otherwise the number is negative.
SQL> SELECT MONTHS_BETWEEN('25-MAY-2009', '15-JAN-2012') FROM dual;
MONTHS_BETWEEN('25-MAY-2009','15-JAN-2012')
-------------------------------------------
-31.677419
SQL>
The next example reverses the same dates and the returned result is a negative number of months:
SQL> SELECT MONTHS_BETWEEN('15-JAN-2012', '25-MAY-2009')FROM dual;
MONTHS_BETWEEN('15-JAN-2012','25-MAY-2009')
-------------------------------------------
31.6774194
SQL>