Uninstalling MySQL on Mac OS X Leopard

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

Use mysqldump to backup your databases to text files!
Stop the database server
sudo rm /usr/local/mysql
sudo rm -rf /usr/local/mysql*
sudo rm -rf /Library/StartupItems/MySQLCOM
sudo rm -rf /Library/PreferencePanes/My*
edit /etc/hostconfig and remove the line MYSQLCOM=-YES-
rm -rf ~/Library/PreferencePanes/My*
sudo rm -rf /Library/Receipts/mysql*
sudo rm -rf /Library/Receipts/MySQL*

The last two lines are particularly important as otherwise, you can’t install an older version of MySQL even though you think that you’ve completely deleted the newer version!