To uninstall MySQL and completely remove it (including all databases) from your Mac do the following:

1. Open a terminal window.

2. Stop the database server.

3. Then run the following commands:

sudo rm /usr/local/mysql
sudo rm -rf /usr/local/mysql*
sudo rm -rf /Library/StartupItems/MySQLCOM
sudo rm -rf /Library/PreferencePanes/My*
rm -rf ~/Library/PreferencePanes/My*
sudo rm -rf /Library/Receipts/mysql*
sudo rm -rf /Library/Receipts/MySQL*
sudo rm -rf /private/var/db/receipts/*mysql*

Linux Instructions are similar:

To uninstall mysql on linux, open terminal and type these commands:

sudo apt-get remove --purge mysql-server mysql-client mysql-common -y
sudo apt-get autoremove -y
sudo apt-get autoclean
rm -rf /etc/mysql
sudo find / -iname 'mysql*' -exec rm -rf {} \;