centos默认安装mysql分支MariaDB，这里安装完整版mysql覆盖mariadb，
首先wget方式下载yum安装使用的Repository包
$ wget http://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
然后yum安装这个包
yum -y install mysql57-community-release-el7-8.noarch.rpm
这时才可以安装mysql
yum -y install mysql-community-server