centos7自带是mariadb，一个mysql的变种。

查看有没有安装过：
yum list installed mysql*
rpm -qa | grep mysql*

安装mysql软件（mariadb）

yum install mysql*

启动mysql
systemctl start mariadb.service 或者 systemctl start mysqld.service

结束
systemctl stop mariadb.service 或者 systemctl stop mysqld.service

重启
systemctl restart mariadb.service 或者 systemctl restart mysqld.service

开机自启
systemctl enable mariadb.service 或者 systemctl enable mysqld.service

centos7.0查看有没有运行mysql