说明
ubuntu 默认是安装mysql 8.x的版本。如果要安装5.7的，可以使用离线安装的方式。
1. 下载mysql
https://dev.mysql.com/downloads/mysql/5.7.html 选择ubuntu18的64位的tar包
mysql-server_5.7.34-1ubuntu18.04_amd64.deb-bundle.tar*
2. 安装
解压后，按如下顺序安装，可能会遇到额外依赖（标红的）。按如下方法安装即可
dpkg -i mysql-common_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i libmysqlclient20_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i libmysqlclient-dev_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i libmysqld-dev_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i libmysqlclient20_5.7.34-1ubuntu18.04_amd64.deb
wget http://security.ubuntu.com/ubuntu/pool/universe/m/mecab/libmecab2_0.996-1.2ubuntu1_amd64.deb
dpkg -i libmecab2_0.996-1.2ubuntu1_amd64.deb
dpkg -i mysql-community-client_5.7.34-1ubuntu18.04_amd64.deb
apt install libtinfo5
dpkg -i mysql-client_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i mysql-community-server_5.7.34-1ubuntu18.04_amd64.deb
dpkg -i mysql-server_5.7.34-1ubuntu18.04_amd64.deb
至此安装成功
3. 修改些配置
修改/etc/mysql/mysql.conf.d下的文件mysqld.cnf
bind-address=xxx
character-set-server=utf8mb4
4. 重启mysql
service mysql restart