（1）参考连接
http://www.cnblogs.com/hld123/p/6603967.html
（2）查看一下是不是有mysql 5.5了
[root@xiaofeibao /]# yum --enablerepo=remi,remi-test list mysql mysql-server
已加载插件：fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
* base: mirror.bit.edu.cn
* epel: mirrors.tuna.tsinghua.edu.cn
* extras: mirror.bit.edu.cn
* remi: mirrors.tuna.tsinghua.edu.cn
* remi-safe: mirrors.tuna.tsinghua.edu.cn
* remi-test: mirrors.tuna.tsinghua.edu.cn
* updates: mirrors.btte.net
remi | 2.9 kB 00:00
remi/primary_db | 1.8 MB 00:00
remi-test | 2.9 kB 00:00
remi-test/primary_db | 538 kB 00:00
已安装的软件包
mysql.x86_64 5.5.57-1.el6.remi @remi
mysql-server.x86_64 5.5.57-1.el6.remi @remi
[root@xiaofeibao /]#
（3）查找以前是否安装有mysql，使用下面命令：
[root@xiaofeibao /]# rpm -qa|grep -i mysql
mysql-libs-5.5.57-1.el6.remi.x86_64
perl-DBD-MySQL-4.013-3.el6.x86_64
mysql-5.5.57-1.el6.remi.x86_64
php-mysqlnd-5.6.31-1.el6.remi.x86_64
mysql-server-5.5.57-1.el6.remi.x86_64
compat-mysql51-5.1.73-1.el6.remi.x86_64
（4）登录mysql、设置密码、
[root@xiaofeibao ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.57 MySQL Community Server (GPL) by Remi
Copyright (c) 2000, 2017, 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>
mysql>
mysql>
mysql>
mysql> grant all privileges on *.* to 'root'@'%' identified by 'sa123456' with grant option;
Query OK, 0 rows affected (0.01 sec)
mysql>
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
（5）查表
mysql> use admin;
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> show tables;
（6）删除用户名
[root@xiaofeibao ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.5.57 MySQL Community Server (GPL) by Remi
Copyright (c) 2000, 2017, 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> 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> desc user;
+------------------------+-----------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+---------+-------+
42 rows in set (0.00 sec)
mysql> select host,user from user;
+------------+------+
| host | user |
+------------+------+
| % | root |
| 127.0.0.1 | root |
| ::1 | root |
| localhost | |
| localhost | root |
| xiaofeibao | |
| xiaofeibao | root |
+------------+------+
7 rows in set (0.02 sec)
mysql> delect from user where host!='%';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'delect from user where host!='%'' at line 1
mysql> delete from user where host!='%';
Query OK, 6 rows affected (0.03 sec)
mysql> delect from user where host!='%';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'delect from user where host!='%'' at line 1
mysql> select host,user from user;
+------+------+
| host | user |
+------+------+
| % | root |
+------+------+
1 row in set (0.00 sec)
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.04 sec)
mysql>
Broadcast message from root@xiaofeibao
(unknown) at 11:34 ...
The system is going down for reboot NOW!