To grant full permissions :
mysql> grant all privileges on database_name.* to 'username'@'localhost';
Query OK, 0 rows affected (0.09 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.09 sec)
mysql -uusername -p
mysql> show databases...
To Revoke all permissions :
mysql> REVOKE ALL PRIVILEGES, GRANT OPTION FROM 'username'@'localhost';