今天遇到一个需求：修改MySQL用户的权限，需要限制特定IP地址才能访问，第一次遇到这类需求，结果在测试过程，使用更新系统权限报发现出现了一些问题， 具体演示如下. 下面测试环境为MySQL 5.6.20. 如有其它版本与下面测试结果有出入，请以实际环境为准。

我们先创建一个测试用户LimitIP，只允许192.168段的IP地址访问，具体权限如下所示：

mysql> GRANT SELECT ON MyDB.* TO LimitIP@'192.168.%' IDENTIFIED BY 'LimitIP';

Query OK, 0 rows affected (0.01 sec)

mysql> GRANT INSERT ,UPDATE,DELETE ON MyDB.kkk TO LimitIP@'192.168.%';

Query OK, 0 rows affected (0.00 sec)

mysql>

mysql> flush privileges;

Query OK, 0 rows affected (0.00 sec)

mysql>

mysql> show grants for LimitIP@'192.168.%';

+----------------------------------------------------------------------------------------------------------------+

| Grants for LimitIP@192.168.%                                                                                   |

+----------------------------------------------------------------------------------------------------------------+

| GRANT USAGE ON *.* TO 'LimitIP'@'192.168.%' IDENTIFIED BY PASSWORD '*72DDE03E02CC55A9478A82F3F4EBE7F639249DEC' |

| GRANT SELECT ON `MyDB`.* TO 'LimitIP'@'192.168.%'                                                              |

| GRANT INSERT, UPDATE, DELETE ON `MyDB`.`kkk` TO 'LimitIP'@'192.168.%'                                          |

+----------------------------------------------------------------------------------------------------------------+

3 rows in set (0.00 sec)

mysql>

假设现在收到需求：这个用户只允许这个IP地址192.168.103.17访问，于是我打算更新mysql.user表，如下所示：

mysql> select user, host from mysql.user where user='LimitIP';

+---------+-----------+

| user    | host      |

+---------+-----------+

| LimitIP | 192.168.% |

+---------+-----------+

1 row in set (0.00 sec)

mysql> update mysql.user set host='192.168.103.17' where user='LimitIP';

Query OK, 1 row affected (0.02 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> flush privileges;

Query OK, 0 rows affected (0.01 sec)

mysql> select user, host from user where user='LimitIP';

ERROR 1046 (3D000): No database selected

mysql> use mysql;

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

Database changed

mysql> select user, host from user where user='LimitIP';

+---------+----------------+

| user    | host           |

+---------+----------------+

| LimitIP | 192.168.103.17 |

+---------+----------------+

1 row in set (0.00 sec)

mysql> show grants for LimitIP@'192.168.103.17';

+---------------------------------------------------------------------------------------------------------------------+

| Grants for LimitIP@192.168.103.17                                                                                   |

+---------------------------------------------------------------------------------------------------------------------+

| GRANT USAGE ON *.* TO 'LimitIP'@'192.168.103.17' IDENTIFIED BY PASSWORD '*72DDE03E02CC55A9478A82F3F4EBE7F639249DEC' |

+---------------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

上面测试发现，如果这样只修改mysql.user表， 那么之前的权限没有了，如下所示，如果你查询mysql.db、 mysql.tables_priv 发现Host的字段值依然为192.168.%

mysql>  select * from mysql.db where user='LimitIP'\G;

*************************** 1. row ***************************

Host: 192.168.%

Db: MyDB

User: LimitIP

Select_priv: Y

Insert_priv: N

Update_priv: N

Delete_priv: N

Create_priv: N

Drop_priv: N

Grant_priv: N

References_priv: N

Index_priv: N

Alter_priv: N

Create_tmp_table_priv: N

Lock_tables_priv: N

Create_view_priv: N

Show_view_priv: N

Create_routine_priv: N

Alter_routine_priv: N

Execute_priv: N

Event_priv: N

Trigger_priv: N

1 row in set (0.00 sec)

ERROR:

No query specified

mysql> select * from mysql.tables_priv where user='LimitIP'\G;

*************************** 1. row ***************************

Host: 192.168.%

Db: MyDB

User: LimitIP

Table_name: kkk

Grantor: root@localhost

Timestamp: 0000-00-00 00:00:00

Table_priv: Insert,Update,Delete

Column_priv:

1 row in set (0.00 sec)

ERROR:

No query specified

所以我继续修改 mysql.db、 mysql.tables_priv 表，然后测试验证终于OK了(请见下面测试步骤)，当然如果账户的权限不止这几个层面，你可能还必须修改例如mysql.columns_priv、mysql.procs_priv等表

mysql> show grants for LimitIP@'192.168.%';

ERROR 1141 (42000): There is no such grant defined for user 'LimitIP' on host '192.168.%'

mysql>

mysql>

mysql> update mysql.db set host='192.168.103.17' where user='LimitIP';

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> update mysql.tables_priv set host='192.168.103.17' where user='LimitIP';

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

mysql> flush privileges;

Query OK, 0 rows affected (0.00 sec)

mysql> show grants for LimitIP@'192.168.103.17';

+---------------------------------------------------------------------------------------------------------------------+

| Grants for LimitIP@192.168.103.17                                                                                   |

+---------------------------------------------------------------------------------------------------------------------+

| GRANT USAGE ON *.* TO 'LimitIP'@'192.168.103.17' IDENTIFIED BY PASSWORD '*72DDE03E02CC55A9478A82F3F4EBE7F639249DEC' |

| GRANT SELECT ON `MyDB`.* TO 'LimitIP'@'192.168.103.17'                                                              |

| GRANT INSERT, UPDATE, DELETE ON `MyDB`.`kkk` TO 'LimitIP'@'192.168.103.17'                                          |

+---------------------------------------------------------------------------------------------------------------------+

3 rows in set (0.00 sec)

mysql>

如果需要修改用户的IP限制，其实更新mysql相关权限表不是上上策，其实有更好的方法，那就是RENAME USER Syntax

mysql> RENAME USER 'LimitIP'@'192.168.103.17' TO 'LimitIP'@'192.168.103.18';

Query OK, 0 rows affected (0.00 sec)

mysql> FLUSH PRIVILEGES;

Query OK, 0 rows affected (0.00 sec)

mysql> show grants for 'LimitIP'@'192.168.103.18';

+---------------------------------------------------------------------------------------------------------------------+

| Grants for LimitIP@192.168.103.18                                                                                   |

+---------------------------------------------------------------------------------------------------------------------+

| GRANT USAGE ON *.* TO 'LimitIP'@'192.168.103.18' IDENTIFIED BY PASSWORD '*72DDE03E02CC55A9478A82F3F4EBE7F639249DEC' |

| GRANT SELECT ON `MyDB`.* TO 'LimitIP'@'192.168.103.18'                                                              |

| GRANT INSERT, UPDATE, DELETE ON `MyDB`.`kkk` TO 'LimitIP'@'192.168.103.18'                                          |

+---------------------------------------------------------------------------------------------------------------------+

3 rows in set (0.00 sec)

mysql>