How to fix login issues with a password-less root MySQL user?

If you installed MySQL without a root password, you will have difficulties to login as root. For example, you need to sudo first, and can’t login as a regular user. The solution to this problem is to create a new root-like user like so:

CREATE USER admin@localhost IDENTIFIED BY 'SOME_PASSWORD';
GRANT ALL PRIVILEGES ON *.* TO admin@localhost WITH GRANT OPTION;

To allow this new user to login from another host, repeat the 2 commands above, replacing localhost with %. Please note that this is not recommended for security reasons.