name | age |
zhangsan | 1 |
lisi | NULL |
wangwu | 2 |
执行一下sql:
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
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:
select * from t_user order by age is null, age;
等价于:
select * from (select name, age, (age is null) as isnull from t_user) as foo order by isnull, age;
看出来了吗?