mysql> grant all on book.* to mk1@localhost identified by "123456";
 #允许访问book数据库下的所有表， 只能访问book表，而且是同一个服务器的用户

mysql> grant all privileges on *.* to mk2@'%' identified by '123456' with grant option;
# with grant option 意思是mk2用户可以把自己的权限下放给新创建的用户。 另外，加不加privileges都可以。%指的任意远程主机，不包括本地地址和localhost
Flush privileges； 刷新数据库 

[root@xuegod64 ~]# mysql -u mk2 -h 192.168.1.63 -p123456
mysql>  #登录正常

[root@xuegod63 ~]# mysql -u mk2 -h 192.168.1.63 -p123456 #不能登录

mysql> grant all privileges on *.* to 'mk2'@'192.168.1.63' identified by '123456' with grant option;
 [root@xuegod63 ~]# mysql -u mk2 -p123456  #不能登录

mysql> grant all privileges on *.* to 'mk2'@'localhost' identified by '123456' with grant option;

mysql> grant select,insert,update,delete,create,drop on aa.* to 'custom'@'localhost' identified by '123456';

mysql> use mysql；
mysql> insert into user (Host,User,Password) values('localhost','grace','123456');
mysql> select Host,User,Password from user where User="grace";
+-----------+-------+----------+
| Host   | User | Password |
+-----------+-------+----------+
| localhost | grace | 123456  |
+-----------+-------+----------+

mysql> insert into user (Host,User,Password) values('localhost','grace1',password("123456"));
Query OK, 1 row affected, 3 warnings (0.00 sec)
mysql> select Host,User,Password from user where User="grace1";
+-----------+--------+-------------------------------------------+
| Host   | User  | Password                 |
+-----------+--------+-------------------------------------------+
| localhost | grace1 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-----------+--------+-------------------------------------------+
1 row in set (0.01 sec)
mysql> flush privileges;  #刷新权限表，使配置文件生效

[root@xuegod63 ~]# service mysqld restart

[root@xuegod63 ~]# mysql -u grace -p123456 #登录不成功
ERROR 1045 (28000): Access denied for user 'grace'@'localhost' (using password: YES)
[root@xuegod63 ~]# mysql -u grace1 -p123456 #登录成功

[root@xuegod63 mysql]# mysqladmin -u root -h 192.168.1.63 password '123'
[root@xuegod63 mysql]# mysql -u root -h 192.168.1.63 -p123

[root@xuegod63 ~]# mysqladmin -u root password '123456' -p123

mysql> SET PASSWORD FOR 'grace1'@'localhost' = PASSWORD('123456');
#注，你的mysql库中已经有记录：grace1'@'localhost
mysql> set password = password ('1234567');
mysql> FLUSH PRIVILEGES;

[root@xuegod63 mysql]# /etc/init.d/mysqld stop
[root@xuegod63 mysql]# mysqld_safe --skip-grant-tables --skip-networking

[root@xuegod63 aa]# mysql   #执行
mysql> update mysql.user set password=password('123456') where host='localhost' and user='root';
[root@xuegod63 aa]# /etc/init.d/mysqld restart
Stopping mysqld:                      [ OK ]