为什么mysql设置了密码之后,不需要输入密码就可以登录数据库了？

CentOS安装mysql之后，之前设置了密码，但输入mysql -u -p后，会直接进入mysql，而输入mysql -uroot -p，则需要输入密码，这是为什么呢？

[[email protected] ~]# mysql -u -p
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.1.73 Source distribution

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> quit
Bye
[[email protected] ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.1.73 Source distribution

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
           

通过查找资料，原来是因为数据库里面有空用户。

解决方法如下：

进入mysql输入：

select * from mysql.user where user='';

mysql> select * from mysql.user where user='';
+-----------+------+----------+-------------+-------------+-------------+-------------+----------------+-----------+------------+-----------------+------------+------------+--------------+----------------+-----------------+------------------+------------------+----------------+--------------------+--------------+----------+------------+-------------+--------------+---------------+-----
| Host      | User | Password | Select_priv | Insert_priv | Update_priv | Delete_priv | Create_pr_priv | File_priv | Grant_priv | References_priv | Index_priv | Alter_priv | Show_db_priv | Supercute_priv | Repl_slave_priv | Repl_client_priv | Create_view_priv | Show_view_priv | Create_routit_priv | Trigger_priv | ssl_type | ssl_cipher | x509_issuer | x509_subject | max_questions | max_
+-----------+------+----------+-------------+-------------+-------------+-------------+----------------+-----------+------------+-----------------+------------+------------+--------------+----------------+-----------------+------------------+------------------+----------------+--------------------+--------------+----------+------------+-------------+--------------+---------------+-----
| localhost |      |          | N           | N           | N           | N           | N              | N         | N          | N               | N          | N          | N            | N              | N               | N                | N                | N              | N                  | N            |          |            |             |              |             0 |     
| hadoop01  |      |          | N           | N           | N           | N           | N              | N         | N          | N               | N          | N          | N            | N              | N               | N                | N                | N              | N                  | N            |          |            |             |              |             0 |     
+-----------+------+----------+-------------+-------------+-------------+-------------+----------------+-----------+------------+-----------------+------------+------------+--------------+----------------+-----------------+------------------+------------------+----------------+--------------------+--------------+----------+------------+-------------+--------------+---------------+-----
2 rows in set (0.00 sec)
           

查询有结果，然后进行下一步。

use mysql;

delete from user where user = '';

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> delete from user where user = '';
Query OK, 2 rows affected (0.00 sec)
           

删除了多余的空白账户， 然后进行下一步。

flush privileges;­

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
           

重载一次权限表,最后用

service mysqld restart

[[email protected] ~]# service mysqld restart
Stopping mysqld:                                           [  OK  ]
Starting mysqld:                                           [  OK  ]
           

重启mysql服务，问题得到解决，

[[email protected] ~]# mysql -u -p
ERROR 1045 (28000): Access denied for user '-p'@'localhost' (using password: NO)
[[email protected] ~]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.1.73 Source distribution

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> quit;
Bye
           

注意：

1、一定要记住重启mysql服务，否则不会生效。

2、msyql的用户表在mysql数据库中的user表中，主要字段有host，user，password等，作为mysql用的管理的主要表。