语法:
--向下递归遍历
select * from tablename start with cond1
connect by cond2
where cond3;
select *
from Table
start with id = 1 //以哪个ID为开始,即跟节点ID
connect by prior id = parent_id //链接通过前一个ID和现在的父ID相等,定义子节点和父节点的关系
order by id ; //排个序