ORACLE SQL 递归、分级查询

第十九章:分级查询

select level,ename

from emp

start with ename='KING'

connect by prior empno=mgr;

start with 子句决定了爬树的起点

connect by prior 主键＝外键 子句决定了爬树的方向:

主键在前是从上向下爬（反之亦反）

col ename for a30

select level,lpad(ename,length(ename)+level*2-2,' ') ename

from emp

start with ename='KING'

connect by prior empno=mgr;

树状结构平铺:

select sys_connect_by_path(ename,'/') ename

from emp

start with ename='KING'

connect by prior empno=mgr

and ename!='BLAKE';

剪枝:

剪枝条件出现在where子句，剪一个节点

select level,lpad(ename,length(ename)+level*2-2,' ') ename

from emp

where ename!='BLAKE'

start with ename='KING'

connect by prior empno=mgr;

剪枝条件出现在connect by prior子句，剪一个分支

select level,lpad(ename,length(ename)+level*2-2,' ') ename

from emp

start with ename='KING'

connect by prior empno=mgr

and ename!='BLAKE';