Ubuntu "E: Unable to locate package mysql"

There is no package with the name of 'mysql' in the repositories.

If you would like to to connect other mysql servers, you need the mysql-client package: sudo apt-get install mysql-client.

If you want to host a database you need the mysql-server package: sudo apt-get install mysql-server.

Installation guide: https://www.digitalocean.com/community/tutorials/how-to-install-mysql-on-ubuntu-16-04

sudo apt-get update && sudo apt-get dist-upgrade

then

sudo apt-get install mysql-server