oracle数据库查看树结构

select *from wd_dept connect by prior id=parent_dept_id start with id=‘4028810a6d13c741016d13e9c9410003’;//父取子
select *from wd_dept connect by prior id=parent_dept_id start with parent_dept_id=‘4028810a6d13c741016d13e9c9410003’;
select *from wd_dept connect by prior parent_dept_id=id start with parent_dept_id=‘4028810a6d13c741016d13e9c9410003’;//子取父

关键词prior，prior跟父节点列parentid放在一起，就是往父结点方向遍历；prior跟子结点列subid放在一起
，则往叶子结点方向遍历，parentid、subid两列谁放在“=”前都无所谓，关键是prior跟谁在一起。

SELECT  LEVEL,
      
        Wd.Dept_Code,
       
        Wd.Dept_Name,
       
        Wd2.Dept_Name,
       
	Wd.Parent_Dept_Id,
       
	Rownum
  
	FROM Hr.Wd_Dept Wd
  LEFT JOIN Hr.Wd_Dept Wd2
 ON Wd.Parent_Dept_Id = Wd2.Id
 
        CONNECT BY PRIOR Wd.Id = Wd.Parent_Dept_Id
 
        START WITH Wd.Parent_Dept_Id = '-1'
 
        ORDER BY Rownum;