When starting MySQL from System Preferences, clicking start multiple times does not work, and I find that a line of warning is displayed below “Warning the user/local/mysql/data directory is not owned by the mysql user”

Enter the following command in the terminal (password required), then click start

sudo chown -RL root:mysql /usr/local/mysql
sudo chown -RL mysql:mysql /usr/local/mysql/data
sudo /usr/local/mysql/support-files/mysql.server start

The mysql password in MAMP (default root – root) is different from the self-installed mysql password.