Installation

apt-get update
apt-get install wget
mkdir /downloads
cd /downloads
wget wget https://dev.mysql.com/get/mysql-apt-config_0.8.12-1_all.deb
sudo dpkg -i mysql-apt-config_0.8.12-1_all.deb
# if the prompt is closed by accident, run:
sudo dpkg-reconfigure mysql-apt-config

Here, select MySQL 5.7, you will be prompt that Ubuntu 20.04 does not support MySQL 5.7.

Don’t worry, select Ubuntu bionic. Then OK.

sudo apt-get update
apt-cache policy mysql-server

We can see

5.7.35-1ubuntu18.04 500 
   500 http://repo.mysql.com/apt/ubuntu bionic/mysql-5.7 amd64 Packages

Now simulate the installation first, then actually install:

Use the -s flag to simulate an action.

For example: “apt-get -s install “ will simulate installing the package, showing you what packages will be installed and configured.

sudo apt install -s -f mysql-client=5.7* mysql-community-server=5.7* mysql-server=5.7*
sudo apt install -f mysql-client=5.7* mysql-community-server=5.7* mysql-server=5.7*

then:

sudo apt-get install -s mysql-client=5.7.34-1ubuntu18.04
sudo apt-get install mysql-client=5.7.34-1ubuntu18.04
sudo apt-get install -s mysql-community-server=5.7.34-1ubuntu18.04
sudo apt-get install mysql-community-server=5.7.34-1ubuntu18.04

Or simply:

sudo apt-get install -s mysql-server=5.7.35-1ubuntu18.04
sudo apt-get install mysql-server=5.7.35-1ubuntu18.04
mysql -V
mysql -u root -p

As a next-step, you need to check status of your wirefall and open up Port 3306:

sudo ufw status
sudo ufw allow 80
sudo ufw allow 3306

Prevent MySql upgrade

Modify this file:

vi /etc/apt/preferences.d/mysql

File content:

Package: mysql-server
Pin: version 5.7.35-1ubuntu18.04
Pin-Priority: 1001

Package: mysql-client
Pin: version 5.7.35-1ubuntu18.04
Pin-Priority: 1001

Package: mysql-community-server
Pin: version 5.7.35-1ubuntu18.04
Pin-Priority: 1001

Package: mysql-community-client
Pin: version 5.7.35-1ubuntu18.04
Pin-Priority: 1001

Package: mysql-apt-config
Pin: version 0.8.12-1
Pin-Priority: 1001

Try to update mysql-server and you will get notified:

mysql-server is already the newest version (5.7.35-1ubuntu18.04). 
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Run MySQL

mysql -u root -p
select version();
CREATE USER 'michael'@'%' IDENTIFIED BY 'bob';
CREATE USER 'alex'@'%' IDENTIFIED BY 'alice';
select host,user,password_last_changed from mysql.user;

Config privileges

Now flash privileges for non-root users:

mysql -u root -p
use mysql;
select host, user from user; 
update user set host = '%' where user = 'root';
select host, user from user;
flush privileges;

Allow remote access of MySQL:

因为默认3306端口只允许本地访问的，注释掉这行

sudo vi /etc/mysql/mysql.conf.d/mysqld.cnf

# By default we only accept connections from localhost
# bind-address  = 127.0.0.1

Restart MySQL:

service mysql restart
systemctl restart mysql

Install an MySQL client

If you are on ubuntu 18:

sudo apt-get install emma

If you are on ubuntu 20, use DBeaver.

To uninstall

service mysql status
service mysql stop
sudo apt-get purge mysql-server mysql-client mysql-common mysql-server-core-* mysql-client-core-*
sudo rm -rf /etc/mysql /var/lib/mysql
sudo apt autoremove

Ref

https://techexpert.tips/mysql/installing-mysql-5-7-ubuntu-20-04/
https://www.cnblogs.com/wang666/p/10218950.html
https://www.cnblogs.com/chenlove/p/9552438.html