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
wit
