一个月份统计，求解决方法。高手来

一个月份统计，求解决办法。高手来。
表a
z1 z2 z3
2010-07-22 14:55:05.0332010-09-15 18:48:12.0003
2010-07-22 14:57:20.3132010-10-26 05:36:00.0874
....


需要按月统计出。
2010-07
2010-08
2010-09
2010-07
2010-08
2010-09
2010-10
.。。

[解决办法]

SQL code

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 allselect 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_dateorder by a_date            a_date    c_num --------------------------1    2010-07    22    2010-08    23    2010-09    24    2010-10    1