CONNECT BY LEVEL 实现12月统计数据

create table test(j varchar2(10),k varchar2(10),l date);
insert into test values('oracle','xun',to_date('2010-11','YYYY-MM'));
insert into test values('java','luxun',to_date('2010-11','YYYY-MM'));
insert into test values('c','xun',to_date('2010-11','YYYY-MM'))

insert into test values('c','xun',sysdate);
insert into test values('java','xun',sysdate);
insert into test values('c++','xun',sysdate); SELECT b.l 月份, nvl(a.amount, 0) 数量
  FROM (select to_char(l, 'mm')  l, count(*)  amount
          from test
         group by to_char(l, 'mm')) a,
       (SELECT lpad(to_char(LEVEL), 2, '0') l
          FROM dual
        CONNECT BY LEVEL <= 12) b
WHERE b.l = a.l(+)
ORDER BY b.l;
/*
月份    数量
1    0
2    0
3    0
4    0
5    0
6    0
7    0
8    0
9    0
10    0
11    3
12    0
*/