递归应用（best）

--单表递归
select * from (select t.*,level as e from student t
start with id=1
connect by nocycle prior id=pid
) where e=3;
select t.*,level as e from student t
start with id=3
connect by nocycle prior pid=id;--向下查
select t.*,level as e from student t
start with id=3
connect by nocycle prior id=pid;--向上查
--http://maping.iteye.com/blog/327687 多表递归查询