Failure to install mysql on macOS Mojave

MySQL 8 makes big changes compared with previous version 5.7. Downgrading directly to the lower version 5.7 from 8.x won't work.

Solution:

1. Uninstall all MySQLs you've installed.

2. Since you're setting up a new machine, there's no existing database. Just clean up the broken database.

   # brew-installed mysql
   rm -rf /usr/local/var/mysql
   
   # db from the official installed
   # should be located at /usr/local/mysql (I'm not very sure)
   ls -ald /usr/local/*mysql*
   # then delete any folders listed by ls
   

3. You'd better remove the conf file /usr/local/etc/my.cnf as well.

4. Reinstall MySQL.