oracle connect by prior 的用法

  connect by 是结构化查询中用到的，

 示例表:

CREATE TABLE DEPT(
DEPTNO NUMBER(10) NOT NULL,
DEPTNAME VARCHAR2(20),
UPPERDEPTNO NUMBER(10)
)

用法1：从子结点往上查.

select * from dept  start with dept is not null connect by prior upperdeptno=deptno;

用法2: 从父结点往下查.

select * from dept  start with dept is not null connect by upperdeptno = prior deptno;

用法3:去掉某个结点以及这个结点的下层结点，得将条件写到connect by 后边，不能写到where后，写在where后边，只能去掉某个结点.

select * from dept where condition1 start with deptno is not null connect by upperdeptno= prior deptno and condition2

用法3：按层来排序(order siblings by)

select * from dept where condition1 start with deptno is not null connect by upperdeptno = prior deptno and condition2 order siblings by column asc/desc.