集合运算,层次查询

select sal,job from emp where deptno=7839
union
select sal,job from emp_jobhistory where empno=7839

select sal,job from emp where deptno=7839
union all
select sal,job from emp_jobhistory where empno=7839

层次查询

• 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

prior相当于 empno = 7876

• 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

• 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