= null和is null区别
= null
判断某个值是否和空相等
is null和is not null
判断某个值为否为空
举例
select e.name, b.bonus
from employee e
left join bonus b
on e.empId = b.empId
where b.bonus < 1000 or b.bonus is null
select e.name, b.bonus
from employee e
left join bonus b
on e.empId = b.empId
where b.bonus < 1000 or b.bonus = null
本文来自博客园,作者:jsqup,转载请注明原文链接:https://www.cnblogs.com/jsqup/p/15988893.html