Analysis on sorting of null values in mysql

The following table analyzes the sorting of null values in mysql: t_user: name agezhangsan 1 lisi NULLwangwu 2 www.2cto.com execute the SQL: SQL code select * from t_user order by age; name agelisi NULLzhangsan 1 wangwu 2 In fact, we want to put records that are not filled with age at the end. We can run the SQL code select * from t_user order by age is null, age; name agezhangsan 1 wangwu 2 lisi NULL why? It can be understood as follows: SQL code select * from t_user order by age is null, age; equivalent to: SQL code select * from (select name, age, (age is null) as isnull from t_user) as foo order by isnull, age;