1、mariadb和mysql
CentOS 7 已經放棄mysql安裝，而是安裝mariadb。（可能是版權問題）
所以，安裝centos 7安裝mysql不能直接用yum install mysql命令。
需用用如下的操作進行安裝。
2、下載mysql源安裝包
wget http://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
3.安裝mysql源
yum localinstall mysql57-community-release-el7-8.noarch.rpm
4、安裝mysql
yum install mysql-community-server
5、啓動mysql服務
systemctl start mysqld
6.查看mysql的啓動狀態
systemctl status mysqld
7.設置開機啓動
systemctl enable mysqld
systemctl daemon-reload
8.修改密碼
需要先查看默認建立的密碼：
grep 'temporary password' /var/log/mysqld.log
結果可知：
A temporary password is generated for root@localhost: HrtC<+uh>2o1
mysql登錄：
mysql -u root -p
HrtC<+uh>2o1
修改密碼：
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'HrtC<+uh>2o1';
mysql> set password for 'root'@'localhost'=password('自己的密碼');
注意：mysql5.7的密碼策略是：大小寫字母+符號
否則會報錯：
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
9.查看密碼策略
mysql>show variables like ‘%password%’
10.添加允許遠程登錄用戶
grant all privileges on *.* to root@"%" identified by "自己的密碼";