in 的用法

in【属于若干个孤立的值】

select * from emp
    where sal in (1500,3000,5000)
--等价于
select * from emp
    where sal = 1500 or sal = 3000 or sal = 5000

select * form emp
    where sal not in (1500,3000,5000)
--等价于
select * from emp
    where sal <> 1500 and sal <> 3000 and sal <> 5000