To completely uninstall MySql OS X it is neccessary to remove numerous files.
You unable to install an older version of MySql even though you thought you have removed everything.
To uninstall MySQL and completely remove it (including all databases) from your Mac do the following:
- Open a terminal window
- 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!