between的用法

select * from emp where sal >= 1500 and sal <=3000
等价于
select * from emp
where sal between 1500 and 3000

--查找工资小于1500或大于3000之间所有员工信息
select * from emp where sal <=1500 or sal <=3000
等价于
select * from emp where sal not between 1500 and 3000