1、在MySQL官网中下载YUM源rpm安装包：http://dev.mysql.com/downloads/repo/yum/
wget http://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
2、yum localinstall mysql57-community-release-el7-8.noarch.rpm
3、yum install mysql-community-server
cp /etc/my.cnf /etc/my.cnf.bak
4、systemctl start mysqld
systemctl status mysqld
5、
systemctl enable mysqld
systemctl daemon-reload
6、mysql安装完成之后，在/var/log/mysqld.log文件中给root生成了一个默认密码。
通过下面的方式找到root默认密码，然后登录mysql进行修改：
grep 'temporary password' /var/log/mysqld.log
mysql -uroot -p
ALTER USER 'root'@'localhost' IDENTIFIED BY 'Liushiqi@2018';
show variables like '%password%';
validate_password_policy：密码策略，默认为MEDIUM策略
validate_password_dictionary_file：密码策略文件，策略为STRONG才需要
validate_password_length：密码最少长度
validate_password_mixed_case_count：大小写字符长度，至少1个
validate_password_number_count ：数字至少1个
validate_password_special_char_count：特殊字符至少1个
上述参数是默认策略MEDIUM的密码检查规则。
7 修改mysql密码策略
set global validate_password_policy=0;
set global validate_password_mixed_case_count=0;
set global validate_password_number_count=3;
set global validate_password_special_char_count=0;
set global validate_password_length=3;
SHOW VARIABLES LIKE 'validate_password%';
SET PASSWORD FOR 'root'@'localhost' = PASSWORD('123456');