层次查询

• PRIOR ：之前的
• 从员工7876出发向上查看

select empno, ename, job, mgr
from emp 
start with empno = 7876
connect by prior mgr = empno

• 从员工KING出发向下查看

select level, ename ||'work for' ||prior ename
from emp 
start with ename='KING'
connect by prior empno = mgr
order by level

• lpad（列名，总长度，列名对应的值不足总长度的话，左边补充的字符）
• where ename<>'JONES' 不显示JONES
• connect by中加入ename<>'JONES'意思是不显示JONES之后的所有人