先删除以前的老版本，注意有数据及时备份。
service mysqld stop

service mysql stop
yum remove mysql-community-server -y
rm -rf /usr/lib/mysql
rm -rf /usr/share/mysql
rm -rf /var/lib/mysql

rm -rf /usr/lib64/mysql

下载rpm包
wget http://yum.osyum.com/linux/mysql/mysql57-community-release-el6-9.noarch.rpm
安装rpm包
rpm -ivh mysql57-community-release-el6-9.noarch.rpm --force --nodeps
安装mysql5.7
yum -y install mysql-community-server 
开启运行mysql5.7
service start mysqld
查看mysqlroot密码
grep "password" /var/log/mysqld.log
进入root修改密码，并把密码长度和复杂密码去掉
mysql -u root -p
密码
ALTER USER 'root'@'localhost' IDENTIFIED BY 'waefwef*1e/';
set global validate_password_policy=0;
set global validate_password_length=1;
FLUSH PRIVILEGES;
quit