http://stackoverflow.com/questions/4359131/brew-install-mysql-on-mac-os/6378429#6378429
brew doctor and fix any errors
brew update
brew install mysql
unset TMPDIR
mysql_install_db --verbose --user=`whoami` --basedir="$(brew --prefix mysql)" --datadir=/usr/local/var/mysql --tmpdir=/tmp
mysql.server start
run the commands Brew suggests, add MySQL to launchctl so it automatically launches at startup
http://soatechlab.blogspot.com/2011/01/completely-remove-mysql-on-mac-os-x.html
ps -ax | grep mysql
stop and kill any MySQL processes
brew remove mysql
brew cleanup
sudo rm /usr/local/mysql
sudo rm -rf /usr/local/var/mysql
sudo rm -rf /usr/local/mysql*
sudo rm ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
sudo rm -rf /Library/StartupItems/MySQLCOM
sudo rm -rf /Library/PreferencePanes/My*
launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
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*
restart your computer just to ensure any MySQL processes are killed try to run mysql, it shouldn't work