mysql> create user test@‘%‘ identified by ‘123456‘;                    创建了用户，但是没有任何权限
Query OK, 0 rows affected (0.00 sec)
mysql> grant all on *.* to root@‘localhost‘ identified by ‘123456‘;    没有用户，则创建用户，用户存在，就赋予权限
Query OK, 0 rows affected (0.00 sec)

mysql> drop user test;                                              
Query OK, 0 rows affected (0.00 sec)