partition outer join实现将稀疏数据转为稠密数据,举例：
with t as
(select deptno, job, sum(sal) sum_sal from emp group by deptno, job),
tt as
(select distinct job from t)
select b.deptno, a.job, sum_sal
from tt a
left join t b partition by (b.deptno)
on a.job = b.job
数据显示结果：
按照所有deptno和job显示出sal总值，没有对应值显示为空。
具体资料参考：
http://blog.sina.com.cn/s/blog_4cef5c7b01016lm5.html