If you look through the MySQL support docs, there is no clear description for uninstalling MySQL in OS X. Here’s how:

Make sure MySQL isn’t running. If you have the preference pane installed, stop the server. Otherwise you can stop it from the terminal:

sudo /Library/StartupItems/MySQLCOM/MySQLCOM stop

Edit /etc/hostconfig

sudo nano /etc/hostconfig
Password:

AFPSERVER=-NO-
AUTHSERVER=-NO-
TIMESYNC=-NO-
QTSSERVER=-NO-
MYSQLCOM=-YES-

Remove or comment out (# marks the line as a comment) the line that says “MYSQLCOM=-YES-”.

Remove MySQL
Still in the terminal….

sudo rm /usr/local/mysql
sudo rm -rf /usr/local/mysql*
sudo rm -rf /Library/StartupItems/MySQLCOM
sudo rm -rf /Library/PreferencePanes/My*
sudo rm -rf /Library/Receipts/mysql*
sudo rm -rf /Library/Receipts/MySQL*
sudo rm -rf /var/db/receipts/com.mysql.*
sudo rm /etc/my.cnf

That’s it. MySQL is gone.