注意事項：
1. 卸載yum MYSQL
systemctl status mysql
systemctl stop mysql
systemctl disable mysqld
rpm -qa | grep -i mysql
yum remove mysql-community-server-5.6.40-2.el7.x86_64
yum -y remove mysql-community-*
rpm -qa | grep -i mysql
find / -name mysql | xargs rm -rf
rm -rf /var/lib/mysql
rm -rf /var/lib/mysql/mysql
rm -rf /usr/share/mysql