查询员工信息：职位与7566员工一样，薪水大于7782员工的薪水 单行
select *
from emp
where job=(select job from emp where empno=7566) and
sal>(select sal from emp where empno=7782)
相关子查询，员工sal大于本部门sal
select rownum,empno,ename,sal,(select avg(sal) from emp where deptno=e.deptno ) avgsal
from emp e
where sal>(select avg(sal) from emp where deptno=e.deptno)
