mysql中null值的排序问题分析_MySQL

mysql中null值的排序问题分析

如下表t_user：

name age

zhangsan 1

lisi NULL

wangwu 2

执行一下sql：

Sql代码

select * from t_user order by age;

name age

lisi NULL

zhangsan 1

wangwu 2

实际上我们是想将没有填写age的记录放在最后，我们可以

Sql代码

select * from t_user order by age is null, age;

name age

zhangsan 1

wangwu 2

lisi NULL

为什么会这样？可以这样来理解：

Sql代码

select * from t_user order by age is null, age;

等价于:

Sql代码

select * from (select name, age, (age is null) as isnull from t_user) as foo order by isnull, age;