select a_date,count(a_date) c_num from (
with t1 as(
select date'2010-07-22' b_date,date'2010-09-15' e_date from dual union all
select date'2010-07-22',date'2010-10-26' from dual )
select to_char(a_date,'yyyy-mm') a_date from (
SELECT ADD_MONTHS(DATE'2009-12-01',LEVEL) AS a_date
    FROM DUAL
   CONNECT BY LEVEL <= 12),t1 
where a_date between ADD_MONTHS(b_date,-1) and e_date)
group by a_date
order by a_date
       
     a_date    c_num 
--------------------------
1    2010-07    2
2    2010-08    2
3    2010-09    2
4    2010-10    1