The MySQL is the open source Database system available for Linux and can be installed on Windows too. The reason for removing or uninstalling the MySQL server completely could be different from user to user but the commands to perform will be the same on Linux.
Here are the commands to uninstall MySQL database server from Ubuntu or Debian based Linux systems:
sudo service mysql stop
sudo apt-get remove --purge mysql*
sudo apt-get autoremove
sudo apt-get autoclean
sudo rm -rf /var/lib/mysql
sudo rm -rf /etc/mysql