oracle distinct、group by、union all叠加使用报错 ?报错

分组聚合条件下，计算xjh不重复的记录条数以及所有记录条数：
with a as(
select '2012' xn,'a'xxdm,'x1' xjh from dual
union all
select '2012' xn,'a'xxdm,'x1' xjh from dual
union all
select '2012' xn,'a'xxdm,'x2' xjh from dual
union all
select '2012' xn,'a'xxdm,'x3' xjh from dual
)
select xn,xxdm,count(distinct xjh)rs
from a
group by xn,xxdm
union all
select xn,xxdm,count( xjh)rs
from a
group by xn,xxdm

在oracle 中执行报错：ora-03113 :通信通道的文件结尾
但删除union all 之后的语句，可正常显示，或删除count()中的distinct 也可执行

求大神指教。