mysql中null值的排序問題分析

mysql中null值的排序問題分析   如下表t_user：  name age zhangsan 1 lisi NULL wangwu 2   www.2cto.com   執行一下sql：  Sql代碼   select * from t_user order by age;     name age lisi NULL zhangsan 1 wangwu 2   實際上我們是想將沒有填寫age的記錄放在最後，我們可以  Sql代碼   select * from t_user order by age is null, age;     name age zhangsan 1 wangwu 2 lisi NULL   為什麼會這樣？可以這樣來理解：  Sql代碼   select * from t_user order by age is null, age;     等價於:  Sql代碼   select * from (select name, age, (age is null) as isnull from t_user) as foo order by isnull, age;