简述
Linux Centos7.x 操作系统版本下针对Mysql的安装和使用多少跟之前的Centos6之前版本有所不同的，下面介绍下在centos7.x环境里安装mysql5.7的几种方法：
一、yum方式安装
从CentOS 7.0发布以来，yum源中开始使用Mariadb来代替MySQL的安装。即使你输入的是yum
install
-y mysql , 显示的也是Mariadb的安装内容。
使用源代码进行编译安装又太麻烦。因此，如果想使用yum安装MySQL的话，就需要去下载官方指定的yum源.
yum下载网址为：https:
//dev
.mysql.com
/downloads/repo/yum/
找到Red Hat Enterprise Linux 7 / Oracle Linux 7 (Architecture Independent), RPM Package，单击后面的Download，
在新的页面中单击最下面的No thanks, just start my download.就可以下载到yum源了。
3.1、安装MySQL YUM资源库
[root@jira-wiki ~]# yum localinstall https://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
3.2、安装MySQL 5.7
[root@jira-wiki ~]# yum install -y mysql-community-server
3.3、启动MySQL服务器和MySQL的自动启动
[root@jira-wiki ~]# systemctl start mysqld.service
[root@jira-wiki ~]# systemctl enable mysqld.service
3.4、密码问题
由于MySQL从5.7开始不允许首次安装后使用空密码进行登录！为了加强安全性，系统会随机生成一个密码以供管理员首次登录使用，
这个密码记录在/var/log/mysqld.log文件中，使用下面的命令可以查看此密码：
[root@jira-wiki ~]# cat /var/log/mysqld.log|grep 'A temporary password'
2018-01-24T02:32:20.210903Z 1 [Note] A temporary password is generated for root@localhost: DOqInortw9/<
最后一行冒号后面的部分DOqInortw9/<就是初始密码。
使用此密码登录MySQL:
[root@jira-wiki ~]# mysql -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.21
Copyright (c) 2000, 2018, 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.
使用随机生产的密码登录到服务端后，必须马上修改密码，不然会报如下错误：
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
有两种方法解决上面的报错（如下的123456是修改后的密码）：
mysql> set password=password("123456");
或者
mysql> alter user 'root'@'localhost' identified by '123456';
刷新权限
mysql> flush privileges;
===============================================================================================
如果上面在执行set password=password("123456");命令后出现下面的报错：
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
解决办法：
这个与Mysql 密码安全策略validate_password_policy的值有关，validate_password_policy可以取0、1、2三个值：
0 or LOW Length
1 or MEDIUM Length; numeric, lowercase/uppercase, and special characters
2 or STRONG Length; numeric, lowercase/uppercase, and special characters; dictionary
默认的数值是1，符合长度，且必须含有数字，小写或大写字母，特殊字符。
所以刚开始设置的密码必须符合长度，且必须含有数字，小写或大写字母，特殊字符。
有时候，只是为了自己测试，不想密码设置得那么复杂，譬如说，我只想设置root的密码为123456。
必须修改两个全局参数：
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
修改上面两个参数后，就可以解决这个报错了。
=======================================================================================================
注意一点：
mysql5.7之后的数据库里mysql.user表里已经没有password这个字段了，password字段改成了authentication_string。
所以修改密码的命令如下：
mysql> update mysql.user set authentication_string=password('kevin@123') where user='root';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 1
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
mysql>
=======================================================================================================
查看mysql版本
mysql> select version();
+-----------+
| version() |
+-----------+
| 5.7.21 |
+-----------+
1 row in set (0.00 sec)
mysql>
=======================================================================================================
修改mysql5.7的编码由latin1为utf8
默认编码：
mysql> show variables like "%character%";show variables like "%collation%";
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)
+----------------------+-------------------+
| Variable_name | Value |
+----------------------+-------------------+
| collation_connection | utf8_general_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
+----------------------+-------------------+
3 rows in set (0.01 sec)
调整操作：
[root@jira-wiki ~]# cat /etc/my.cnf
......
[mysqld]
......
character-set-server=utf8 //注意这个不能写成default-character-set=utf8，否则会导致5.7版本mysql无法打开
[client]
default-character-set=utf8
[root@kevin~]# systemctl restart mysqld.service
[root@kevin~]# mysql -p
......
mysql> show variables like "%character%";show variables like "%collation%";
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.01 sec)
+----------------------+-----------------+
| Variable_name | Value |
+----------------------+-----------------+
| collation_connection | utf8_general_ci |
| collation_database | utf8_general_ci |
| collation_server | utf8_general_ci |
+----------------------+-----------------+
3 rows in set (0.00 sec)
mysql>