1. Install yum repo

There is no mysql in the yum source of centos (you can try to use the installation command directly: Yum install mysql server). You need to download the yum repo configuration file on mysql's official website, and then install:

#download
wget https://dev.mysql.com/get/mysql57-community-release-el7-9.noarch.rpm
#repo installation
rpm -ivh mysql57-community-release-el7-9.noarch.rpm

2. Install mysql

yum install mysql-server  #Installation command
systemctl start mysqld    #Start MySQL

3. Operation command set

#Install mysql for the first time and start the operation with notes
systemctl start mysqld #Start MySQL. After the command is executed, there is no return. You can use the status command to check whether the startup is successful
systemctl stop mysqld #Close MySQL
systemctl restart mysqld #Restart MySQL

#Check the running status of MySQL and display active (running) to indicate success
systemctl status mysqld
#Operation example
[root@VM_0_6_centos ~]# systemctl status mysqld
● mysqld.service - MySQL Server
   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2019-03-18 11:25:45 CST; 56s ago

systemctl enable mysqld #Set startup
systemctl disable mysqld #Turn off startup

#For the first installation, you need to obtain a temporary password. The command is as follows. The last colon returned is followed by the temporary password. Here I am: aMKsBq#s-2(Y
grep 'temporary password' /var/log/mysqld.log
#Operation example
[root@VM_0_6_centos ~]# grep 'temporary password' /var/log/mysqld.log
2019-03-18T03:25:37.681423Z 1 [Note] A temporary password is generated for root@localhost: aMKsBq#s-2(Y

#If not, delete the original mysql residual data first. Note: this operation is not required for the first installation
rm -rf /var/lib/mysql
#Restart after deletion
systemctl restart mysqld #Restart MySQL

#Command to log in to mysql. After input, prompt for password. The password is hidden and not displayed. Just copy it in directly. Press enter to log in successfully
mysql -u root -p   #Indicates root account login
#Operation example:
[root@VM_0_6_centos ~]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.25
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> 
#After logging in, you can operate mysql database

4. Installation process problems

Because SSH tool will automatically break if you don't operate it for a long time. When you install mysql to half of the time, you need to select is this OK [y / N]: when you do y, you need to do other things, reopen the tool connection, and then use yum install mysql server to install the following content:

[root@VM_0_6_centos ~]# yum install mysql-server
Loaded plugins: fastestmirror, langpacks
Existing lock /var/run/yum.pid: another copy is running as pid 22795.
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: yum
    Memory :  87 M RSS (482 MB VSZ)
    Started: Mon Mar 18 10:53:34 2019 - 25:01 ago
    State  : Sleeping, pid: 22795

It shows that yum is locked. Solution: see the pid in the first line and kill it directly. Continue to install mysql5.7 normally

[root@VM_0_6_centos ~]# kill -9 22795