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对于oracle进行简单树查询(递归查询)，很早想总结了，发一下了：
通过子节点向根节点追朔.
| DEPTID |
PAREDEPTID |
NAME |
| NUMBER |
NUMBER |
CHAR (40 Byte) |
| 部门id |
父部门id(所属部门id) |
部门名称 |
- 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.
- 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.
- 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
- 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
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