strat with 指定层次开始的条件，即是说满足这个条件的行即可以做为层次树的最顶层
connect by prior指层之间的关联条件，即什么样的行是上层行的子行（自连接条件）
--查询所有子节点 SELECT * FROM hrmdepartment where canceled = 0 START WITH departmentname =‘智能管理部‘ CONNECT BY PRIOR id=supdepid
--查询所有父节点 SELECT * FROM hrmdepartment where canceled = 0 START WITH departmentname =‘开发模块‘ CONNECT BY PRIOR supdepid=id
--查询指定节点的，根节点 SELECT hd.*,connect_by_root(id),connect_by_root(departmentname) FROM hrmdepartment hd where canceled = 0 START WITH departmentname =‘智能管理部‘ CONNECT BY PRIOR id=supdepid
--递归路径 SELECT hd.*,sys_connect_by_path(departmentname,‘->‘) namepath,LEVEL FROM hrmdepartment hd where canceled = 0 START WITH departmentname =‘智能管理部‘ CONNECT BY PRIOR id=supdepid
原文：https://www.cnblogs.com/ooo0/p/13131361.html