第十章层次查询课堂笔记和练习

– 层次查询
– 遍历树

• 从底向上

  1.查询雇员编号为7876的员工信息，以及从底向上的上级经理信息。
      select * from emp where empno = 7876
      union
      select * from emp where empno = 7788
      union
      select * from emp where empno = 7566
      union
      select * from emp where empno = 7839;
  
      select * from emp 
       start with empno=7876 
     connect by prior mgr = empno;--empno 父列  mgr子列（优先级高）
     --  prior 跟谁谁的级别高
      select * from emp 
       start with empno=7876 
     connect by empno = prior mgr;--同上
  

• 从上往下

  --  查询雇员编号为7839的员工信息，并按照从顶向下的顺序查上级经理信息
      select empno, ename, job, mgr
        from emp
       start with empno = 7839
      connect by prior empno = mgr;
  
  --  通过prior关键字，获取上下级员工信息
      select empno, ename, job, mgr,prior ename, prior mgr
        from emp
       strat with empno = 7839
      connect by prior empno = mgr;
  

• LEVEL查看分层等级信息

      select level,e.* 
        from emp e 
       start with ename='KING' 
     connec