Cannpt login as mysql user root from normal user account

 cf: https://askubuntu.com/questions/766334/cant-login-as-mysql-user-root-from-normal-user-account-in-ubuntu-16-04

$ sudo mysql -u root

mysql> DROP USER 'root'@'localhost';

mysql> CREATE USER 'root'@'localhost' IDENTIFIED BY '<root_password>';

mysql> GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION; 

mysql> FLUSH PRIVILEGES;

In above, One replace 'root' e.g. with 'chiao' to create the a mysql user as root.