oracle hierarchical query（分级查询）

hierarchical_query_clause

1. Hierarchical Query Operators :PRIOR、CONNECT_BY_ROOT.
2. Hierarchical Query Pseudocolumns :CONNECT_BY_ISCYCLE、CONNECT_BY_ISLEAF、LEVEL. 
3. You can specify CONNECT_BY_ISCYCLE only if you have specified the NOCYCLE parameter of the CONNECT BY clause.

select t.dept_name "AreaName",
       connect_by_root t.dept_name "Root",
       connect_by_isleaf "isLeaf",
       connect_by_iscycle "isCycle",
       level,
       Sys_connect_by_path(t.dept_name, '/') "Path"
  from rs_dept t
/*where level = 4*/
 start with t.upper_dept_id = '1'
connect by nocycle prior t.dept_id = t.upper_dept_id