a、演示双空用户登陆[root@xlkoracel ~]# mysql -uroot -pEnter password: (root@localhost) [(none)]> show variables like 'version';+---------------+--------+| Variable_name | Value  |+---------------+--------+| version       | 5.6.26 |+---------------+--------+(root@localhost) [(none)]> select user,host,password from mysql.user;+-------+-------------+-------------------------------------------+| user  | host        | password                                  |+-------+-------------+-------------------------------------------+| root  | localhost   | *E74858DB86EBA20BC33D0AECAE8A8108C56B17FA || root  | xlkoracel   |                                           || root  | 127.0.0.1   |                                           || root  | ::1         |                                           ||       | localhost   |                                           ||       | xlkoracel   |                                           || mycat | localhost   | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD || mycat | 192.168.1.% | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD || mycat | 192.168.%.% | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD || root  | 192.168.%.% | *E74858DB86EBA20BC33D0AECAE8A8108C56B17FA |+-------+-------------+-------------------------------------------+(root@localhost) [(none)]> -- 可以看到存在用户名和密码同时为空的情形(root@localhost) [(none)]> -- 退出后尝试使用任意用户名登录(root@localhost) [(none)]> exitBye[root@xlkoracel ~]# mysql -uxx ###无需指定密码参数-p(xx@localhost) [(none)]> -- 可以成功登陆(xx@localhost) [(none)]> -- 下面查看一下自身的权限(xx@localhost) [(none)]> show grants;  --当前只有usage权限+--------------------------------------+| Grants for @localhost                |+--------------------------------------+| GRANT USAGE ON *.* TO ''@'localhost' |+--------------------------------------+(xx@localhost) [(none)]> show databases;+--------------------+| Database           |+--------------------+| information_schema || test               |+--------------------+(xx@localhost) [(none)]> use test;Database changed(xx@localhost) [test]> show tables;Empty set (0.00 sec)(xx@localhost) [test]> create table t(id int);Query OK, 0 rows affected (0.14 sec)(xx@localhost) [test]> insert into t values(1);Query OK, 1 row affected (0.01 sec)(xx@localhost) [test]> select * from t;+------+| id   |+------+|    1 |+------+1 row in set (0.00 sec)(xx@localhost) [test]> --从上可以看出，usage权限已经可以完成很多任务(xx@localhost) [test]> use infromation_schema;ERROR 1044 (42000): Access denied for user ''@'localhost' to database 'infromation_schema'(xx@localhost) [test]> exit;b、演示密码为空的用户登陆[root@xlkoracel ~]# mysql -uroot -hxlkoracel  ###注，此时也无需指定参数-p  (root@xlkoracel) [(none)]> --可以成功登陆(root@xlkoracel) [(none)]> show grants;   --查看自身权限，为ALL PRIVILEGES，权限更大+---------------------------------------------------------------------+| Grants for root@xlkoracel                                           |+---------------------------------------------------------------------+| GRANT ALL PRIVILEGES ON *.* TO 'root'@'xlkoracel' WITH GRANT OPTION || GRANT PROXY ON ''@'' TO 'root'@'xlkoracel' WITH GRANT OPTION        |+---------------------------------------------------------------------+

[root@xlkoracel ~]# mysql -uroot -pEnter password: (root@localhost) [(none)]> select user,host,password from mysql.user    -> where (user is null or user='') and (password is null or password='');+------+-----------+----------+| user | host      | password |+------+-----------+----------+|      | localhost |          ||      | xlkoracel |          |+------+-----------+----------+2 rows in set (0.01 sec)(root@xlkoracel) [(none)]> -- Author : Leshami(root@xlkoracel) [(none)]> -- Blog   : http://blog.csdn.net/leshami(root@localhost) [(none)]> -- 使用drop 方式清理用户(root@localhost) [(none)]> drop user ''@'localhost';Query OK, 0 rows affected (0.24 sec)(root@localhost) [(none)]> select user,host,password from mysql.user    -> where (user is null or user='') and (password is null or password='');+------+-----------+----------+| user | host      | password |+------+-----------+----------+|      | xlkoracel |          |+------+-----------+----------+1 row in set (0.00 sec)(root@localhost) [(none)]> -- 直接用delete从mysql.user表清理用户(root@localhost) [(none)]> delete from mysql.user    -> where (user is null or user='') and (password is null or password='');Query OK, 1 row affected (0.06 sec)(root@localhost) [(none)]> -- 直接用delete从mysql.user表清理所有密码为空的用户(root@xlkoracel) [(none)]> delete from mysql.user where password is null or password='';Query OK, 3 rows affected (0.00 sec)