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*
- sudo rm -rf /private/var/db/receipts/*mysql*
The last three 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!