ORACLE递归查询

对于oracle进行简单树查询(递归查询) 
DEPTID PAREDEPTID NAME 
NUMBER NUMBER CHAR (40 Byte) 
部门id 父部门id(所属部门id) 部门名称 


通过子节点向根节点追朔. 

Sql代码 
select * from persons.dept start with deptid=76 connect by prior paredeptid=deptid   

select * from persons.dept start with deptid=76 connect by prior paredeptid=deptid  

通过根节点遍历子节点. 

Sql代码 
select * from persons.dept start with paredeptid=0 connect by prior deptid=paredeptid   

select * from persons.dept start with paredeptid=0 connect by prior deptid=paredeptid  

可通过level 关键字查询所在层次. 

Sql代码 
select a.*,level from persons.dept a start with paredeptid=0 connect by prior deptid=paredeptid   

select a.*,level from persons.dept a start with paredeptid=0 connect by prior deptid=paredeptid  

再次复习一下:start with ...connect by 的用法, start with 后面所跟的就是就是递归的种子。 

递归的种子也就是递归开始的地方 connect by 后面的"prior" 如果缺省:则只能查询到符合条件的起始行,并不进行递归查询; 

connect by prior 后面所放的字段是有关系的,它指明了查询的方向。 

练习: 通过子节点获得顶节点 

Sql代码 
select FIRST_VALUE(deptid) OVER (ORDER BY LEVEL DESC ROWS UNBOUNDED PRECEDING) AS firstdeptid from persons.dept start with deptid=76 connect by prior paredeptid=deptid  
posted @ 2012-06-28 11:19  blogs_lw  阅读(254)  评论(0编辑  收藏  举报