year_of_calendar,
month_of_year
FROM
sys_calendar.calendar
WHERE
calendar_date<=current_date AND EXTRACT(month FROM calendar_date)<> EXTRACT(MONTH FROM current_date) AND
--because you want last 6 months and not current month
calendar_date>current_date-INTERVAL '6' MONTH
GROUP BY 1,2
ORDER BY 1 DESC, 2 DESC;
Results set look like this:
Yr Mo
2010 03
2010 02
2010 01
2009 12
2009 11
2009 10
