子查询
大于30号部门最高工资的所有员工信息(2种写法)
select * from emp where sal>all(select sal from emp e2 where deptno=30)
select * from emp e where sal>(select max(sal) from emp e2 where deptno=30)
select * from emp e where (job,sal) = (select job,sal from emp where ename='ALLEn')
select * from emp e where job=(select job from emp where ename='ALLEn') and sal=(select sal from emp where ename='ALLEn')