新浪的镜像站
http://mirrors.sohu.com/mysql
yum安装：
首先要到MySQL yum库的下载页面http://dev.mysql.com/downloads/repo/yum/
下载：mysql57-community-release-el7-11.noarch.rpm
安装：rpm -Uvh mysql57-community-release-el7-9.noarch.rpm
yum安装server：
yum install mysql-community-server
yum安装client：
yum install mysql-community-client
yum-config-manager --disable mysql80-community #关闭mysql8的仓库
yum-config-manager --enable mysql57-community #打开mysql5.7的仓库
mysql56 #5.6的仓库
mysql55 #5.5的仓库