Let’s talk about accounts and permissions in mysql
- WBOYforward
- 2022-01-14 17:10:072332browse
This article brings you issues related to account permissions in MySQL. When a user performs any database operation, the server will verify whether the user has the corresponding permissions. For example, querying tables requires SELECT permissions, and deleting objects requires DROP. permissions. I hope everyone has to help.
When the client connects to the MySQL server, it must provide valid authentication, such as username and password. When a user performs any database operation, the server will verify whether the user has the corresponding permissions. For example, querying a table requires SELECT permissions, and deleting objects requires DROP permissions.
In order to facilitate the management of user rights, MySQL 8.0 provides the role function. A role is a collection of permissions.
#In this article we discuss the management of accounts and permissions in MySQL.
5.1 Manage users
5.1.1 Create users
MySQL is created using the CREATE USER statement User, the basic syntax is as follows:
CREATE USER [IF NOT EXISTS] account_name IDENTIFIED BY 'password';
Among them, account_name is the account name; the account name is divided into two parts: user name (user_name) and host name (host_name), using % connection. IDENTIFIED BY is used to specify the user's password. IF NOT EXISTS is used to avoid error messages when creating accounts with the same name.
The following statement creates a new user dev01, which can log in from the local machine (localhost):
mysql> CREATE USER dev01@localhost IDENTIFIED BY 'Dev01@mysql'; Query OK, 0 rows affected (0.21 sec)
The account in MySQL is determined by the user name and the host name, the host office.example.com dev01 on the host and dev01 on the host home.example.com are two accounts. If you do not specify a host name, it means that the user can log in from any host:
user_name user_name@%
% is a wildcard character, representing any string; in addition, _ represents any single character.
If the user name or host name contains special characters, such as spaces or -, you need to use quotation marks to quote the two parts respectively:
'user-name'@'host-name'
In addition to single quotation marks, you can also use backticks (`) or double quotes (").
Account information in MySQL is stored in the user table of the system database mysql:
mysql> select host, user from mysql.user; +-----------+------------------+ | host | user | +-----------+------------------+ | localhost | dev01 | | localhost | mysql.infoschema | | localhost | mysql.session | | localhost | mysql.sys | | localhost | root | +-----------+------------------+ 5 rows in set (0.00 sec)
Except for dev01@localhost, the other four users are Is the system user created initially.
In addition to the basic syntax, you can also specify more options when creating a user:
resource_option: {
MAX_QUERIES_PER_HOUR count
| MAX_UPDATES_PER_HOUR count
| MAX_CONNECTIONS_PER_HOUR count
| MAX_USER_CONNECTIONS count
}resource_option is used to limit the user's use of system resources:
MAX_QUERIES_PER_HOUR, the number of queries allowed to be executed per hour. The default is 0, indicating no limit;
MAX_UPDATES_PER_HOUR, the number of updates allowed to be executed per hour. The default is 0, which means there is no limit;
MAX_CONNECTIONS_PER_HOUR, the number of connections allowed per hour. The default is 0, which means there is no limit;
MAX_USER_CONNECTIONS, the number of concurrent connections for this user. The default is 0, which means there is no limit; at this time, the number of concurrent connections for the user is determined by the system variable max_user_connections.
The following statement creates a new account dev02 , allowing login from any host. At the same time, the user is restricted to perform up to 1000 queries and 100 updates per hour:
mysql> CREATE USER 'dev02'@'%'
-> WITH MAX_QUERIES_PER_HOUR 1000 MAX_UPDATES_PER_HOUR 100;
Query OK, 0 rows affected (0.01 sec)Note that the -> in the second line is the client prompt, not the input content. Query The system user table can display the above settings:
mysql> select host, user, max_questions, max_updates from mysql.user; +-----------+------------------+---------------+-------------+ | host | user | max_questions | max_updates | +-----------+------------------+---------------+-------------+ | % | dev02 | 1000 | 100 | | localhost | dev01 | 0 | 0 | | localhost | mysql.infoschema | 0 | 0 | | localhost | mysql.session | 0 | 0 | | localhost | mysql.sys | 0 | 0 | | localhost | root | 0 | 0 | +-----------+------------------+---------------+-------------+ 6 rows in set (0.00 sec)
The following are the password management options:
password_option: {
PASSWORD EXPIRE [DEFAULT | NEVER | INTERVAL N DAY]
| PASSWORD HISTORY {DEFAULT | N}
| PASSWORD REUSE INTERVAL {DEFAULT | N DAY}
| PASSWORD REQUIRE CURRENT [DEFAULT | OPTIONAL]
}The password management options can be used to set the password expiration policy, reuse policy and verification when changing the password:
PASSWORD EXPIRE, set the password to expire immediately; PASSWORD EXPIRE DEFAULT, use the global password expiration policy, determined by the system variable default_password_lifetime; PASSWORD EXPIRE NEVER, the password will never expire; PASSWORD EXPIRE INTERVAL N DAY password expires every N days;
PASSWORD HISTORY DEFAULT, uses the global password reuse policy, determined by the system variable password_history; PASSWORD HISTORY N, the new password cannot be the same as the last N passwords Repeat;
PASSWORD REUSE INTERVAL DEFAULT, use the global password reuse policy (specified according to the time interval), determined by the system variable password_reuse_interval; PASSWORD REUSE INTERVAL N DAY, the new password is the same as the last N days The password cannot be repeated;
PASSWORD REQUIRE CURRENT, the user needs to enter the current password when changing the password; PASSWORD REQUIRE CURRENT OPTIONAL, the user does not need to enter the current password when changing the password; PASSWORD REQUIRE CURRENT DEFAULT, Use the global policy, determined by the system variable password_require_current.
The password options of the account can also be viewed through the mysql.user table:
mysql> select host,user,
-> password_expired, password_last_changed,
-> password_lifetime, password_reuse_history,
-> password_reuse_time, password_require_current
-> from mysql.user;
+-----------+------------------+------------------+-----------------------+-------------------+------------------------+---------------------+--------------------------+
| host | user | password_expired | password_last_changed | password_lifetime | password_reuse_history | password_reuse_time | password_require_current |
+-----------+------------------+------------------+-----------------------+-------------------+------------------------+---------------------+--------------------------+
| % | dev02 | N | 2019-09-23 15:02:47 | NULL | NULL | NULL | NULL |
| localhost | dev01 | N | 2019-09-23 14:23:39 | NULL | NULL | NULL | NULL |
| localhost | mysql.infoschema | N | 2019-08-28 10:07:39 | NULL | NULL | NULL | NULL |
| localhost | mysql.session | N | 2019-08-28 10:07:39 | NULL | NULL | NULL | NULL |
| localhost | mysql.sys | N | 2019-08-28 10:07:39 | NULL | NULL | NULL | NULL |
| localhost | root | N | 2019-08-28 10:07:44 | NULL | NULL | NULL | NULL |
+-----------+------------------+------------------+-----------------------+-------------------+------------------------+---------------------+--------------------------+
6 rows in set (0.00 sec)The following are the account lock options:
lock_option: {
ACCOUNT LOCK
| ACCOUNT UNLOCK
}This option is used to specify Whether to lock the account, the locked account cannot be used; the default is ACCOUNT UNLOCK, the account is not locked.
5.1.2 Modify the user
ALTER USER statement can modify the user's attributes. The options for modifying the user are the same as creating the user.
The first step is to change the user’s password. The following statement is used to change the password of user dev01:
mysql> ALTER USER dev01@localhost IDENTIFIED BY 'Dev01@2019'; Query OK, 0 rows affected (0.25 sec)
MySQL 提供了 RENAME USER 语句，用于修改用户名：
mysql> RENAME USER dev02 TO dev03; Query OK, 0 rows affected (0.26 sec)
用户 dev02 被重命名为 dev03。
RENAME USER 语句自动将旧用户的权限授予新用户，但是不会自动解决旧用户上的对象依赖。例如，某个存储过程的定义者为旧的用户名，并且使用定义者权限运行时，将会产生错误。
另一个常见的用户修改操作就是锁定账户和解锁账户：
mysql> ALTER USER dev01@localhost ACCOUNT LOCK; Query OK, 0 rows affected (0.13 sec)
用户 dev01 被锁定，此时无法使用该用户进行连接：
"C:\Program Files\MySQL\MySQL Server 8.0\bin\mysql.exe" -u dev01 -p Enter password: ********** ERROR 3118 (HY000): Access denied for user 'dev01'@'localhost'. Account is locked.
系统变量 Locked_connects 用于记录锁定账户尝试登录的次数：
mysql> SHOW GLOBAL STATUS LIKE 'Locked_connects'; +-----------------+-------+ | Variable_name | Value | +-----------------+-------+ | Locked_connects | 1 | +-----------------+-------+ 1 row in set (0.00 sec)
最后我们将 dev01 进行解锁：
mysql> ALTER USER dev01@localhost ACCOUNT UNLOCK; Query OK, 0 rows affected (0.10 sec)
5.1.3 删除用户
DROP USER 语句用于删除一个用户。以下语句将会删除用 dev03：
mysql> DROP USER dev03; Query OK, 0 rows affected (0.14 sec)
如果被删除的用户已经连接到 MySQL 服务器，用户可以继续执行操作；但是无法建立新的连接。
5.2 管理权限
新创建的用户默认只有 USAGE 权限，只能连接数据库，而没有任何操作权限。使用 SHOW GRANTS 命令可以查看用户的权限：
mysql> SHOW GRANTS FOR dev01@localhost; +-------------------------------------------+ | Grants for dev01@localhost | +-------------------------------------------+ | GRANT USAGE ON *.* TO `dev01`@`localhost` | +-------------------------------------------+ 1 row in set (0.00 sec)
使用 GRANT 语句可以为用户授予权限。
5.2.1 授予权限
GRANT 语句基本语法如下：
GRANT privilege, ... ON privilege_level TO account_name;
GRANT 语句支持一次授予多个权限，使用逗号进行分隔。
privilege_level 指定权限的作用级别，包括：
全局权限，作用于 MySQL 服务器中的所有数据库。全局权限使用*.*表示，例如，以下语句授予 dev01@localhost 用户查询所有数据库中的所有表的权限：
mysql> GRANT SELECT -> ON *.* -> TO dev01@localhost; Query OK, 0 rows affected (0.01 sec) mysql> SHOW GRANTS FOR dev01@localhost; +--------------------------------------------+ | Grants for dev01@localhost | +--------------------------------------------+ | GRANT SELECT ON *.* TO `dev01`@`localhost` | +--------------------------------------------+ 1 row in set (0.00 sec)
全局权限存储在 mysql.user 表中。
数据库权限，作用于指定数据库中的所有对象。数据库权限使用db_name.*表示，例如，以下语句授予 dev01@localhost 用户查询数据库 world 中的所有表的权限：
mysql> GRANT ALL
-> ON world.*
-> TO dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+----------------------------------------------------------+
| Grants for dev01@localhost |
+----------------------------------------------------------+
| GRANT SELECT ON *.* TO `dev01`@`localhost` |
| GRANT ALL PRIVILEGES ON `world`.* TO `dev01`@`localhost` |
+----------------------------------------------------------+
2 rows in set (0.00 sec)数据库权限存储在 mysql.db 表中。
表权限，作用于指定表的所有列。数据库权限使用db_name.table_name表示；如果不指定 db_name，使用默认数据库；如果没有默认数据库，将会返回错误。例如，以下语句授予 dev01@localhost 用户数据库 world 中country 表的增删改查权限：
mysql> GRANT SELECT, INSERT, UPDATE, DELETE
-> ON world.country
-> TO dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+----------------------------------------------------------------------------------+
| Grants for dev01@localhost |
+----------------------------------------------------------------------------------+
| GRANT SELECT ON *.* TO `dev01`@`localhost` |
| GRANT ALL PRIVILEGES ON `world`.* TO `dev01`@`localhost` |
| GRANT SELECT, INSERT, UPDATE, DELETE ON `world`.`country` TO `dev01`@`localhost` |
+----------------------------------------------------------------------------------+
3 rows in set (0.00 sec)表权限存储在 mysql.tables_priv 表中。
列权限，作用于指定表的指定列。每个列权限都需要指定具体的列名。例如，以下语句授予 dev01@localhost 用户在 world.country 表中 code 和 name 字段的查询权限，以及 population 字段的修改权限：
mysql> GRANT SELECT(code, name), UPDATE(population)
-> ON world.country
-> TO dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+----------------------------------------------------------------------------------------------------------------------------------+
| Grants for dev01@localhost |
+----------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT ON *.* TO `dev01`@`localhost` |
| GRANT ALL PRIVILEGES ON `world`.* TO `dev01`@`localhost` |
| GRANT SELECT, SELECT (`code`, `name`), INSERT, UPDATE, UPDATE (`population`), DELETE ON `world`.`country` TO `dev01`@`localhost` |
+----------------------------------------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)列权限存储在 mysql.columns_priv 表中。
存储例程权限，作用于存储例程（函数和过程）。存储例程权限可以基于全局、数据库或者单个例程进行指定。以下语句授予 dev01@localhost 用户在数据库 world.country 中创建存储例程的权限：
mysql> GRANT CREATE ROUTINE
-> ON world.*
-> TO dev01@localhost;
Query OK, 0 rows affected (0.02 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for dev01@localhost |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT ON *.* TO `dev01`@`localhost`|
| GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, REFERENCES, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, CREATE VIEW, SHOW VIEW, ALTER ROUTINE, EVENT, TRIGGER ON `world`.* TO `dev01`@`localhost` |
| GRANT SELECT, SELECT (`code`, `name`), INSERT, UPDATE, UPDATE (`population`), DELETE ON `world`.`country` TO `dev01`@`localhost` |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)存储例程权限存储在 mysql.procs_priv 表中。
代理用户权限，允许用户作为其他用户的代理。代理用户拥有被代理用户的所有权限。以下语句将 dev01@localhost 用户设置为 root 用的代理：
mysql> GRANT PROXY
-> ON root
-> TO dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for dev01@localhost |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT ON *.* TO `dev01`@`localhost` |
| GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, REFERENCES, INDEX, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, CREATE VIEW, SHOW VIEW, ALTER ROUTINE, EVENT, TRIGGER ON `world`.* TO `dev01`@`localhost` |
| GRANT SELECT, SELECT (`code`, `name`), INSERT, UPDATE, UPDATE (`population`), DELETE ON `world`.`country` TO `dev01`@`localhost` |
| GRANT PROXY ON 'root'@'%' TO 'dev01'@'localhost' |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
4 rows in set (0.00 sec)代理用户权限存储在 mysql.proxies_priv 表中。
5.2.2 撤销权限
REVOKE 语句执行与 GRANT 语句相反的操作，撤销授予用户的权限。
REVOKE privilegee, .. ON privilege_level FROM account_name;
撤销权限的参数与授予权限时类似，以下语句撤销用户 dev01@localhost 所有的权限：
mysql> REVOKE ALL, GRANT OPTION
-> FROM dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+--------------------------------------------------+
| Grants for dev01@localhost |
+--------------------------------------------------+
| GRANT USAGE ON *.* TO `dev01`@`localhost` |
| GRANT PROXY ON 'root'@'%' TO 'dev01'@'localhost' |
+--------------------------------------------------+
2 rows in set (0.00 sec)代理用户权限需要单独撤销：
mysql> REVOKE PROXY
-> ON root
-> FROM dev01@localhost;
Query OK, 0 rows affected (0.01 sec)
mysql> SHOW GRANTS FOR dev01@localhost;
+-------------------------------------------+
| Grants for dev01@localhost |
+-------------------------------------------+
| GRANT USAGE ON *.* TO `dev01`@`localhost` |
+-------------------------------------------+
1 row in set (0.00 sec)用户 dev01@localhost 又恢复了初始的权限。
对于全局级别的权限，REVOKE 的效果在用户下次登录时生效；对于数据库级别的权限，REVOKE 的效果在执行 USE 命令后生效；对于表级或者字段级别的权限，REVOKE 的效果随后的查询立即生效。
5.3 管理角色
当用户越来越多时，权限的管理也越来越复杂；而实际上，许多用户需要相同或类似的权限。为此，MySQL 8.0 引入了一个新的特性：角色（Role）。角色是一组权限的集合。
与账户类似，角色也可以授予权限；但是角色不能用于登录数据库。通过角色为用户授权的步骤如下：
创建一个角色；
为角色授权权限；
为用户指定角色。
5.3.1 创建角色
假设我们的应用需要使用 world 数据库。开发人员需要该数据库的完全访问权限，测试人员需要表的读写权限，业务分析人员需要查询数据的权限。
首先，使用CREATE ROLE语句创建 3 个角色：
mysql> CREATE ROLE devp_role, read_role, write_role; Query OK, 0 rows affected (0.02 sec)
角色名称和账户名称类似，也可以包含 role_name 和 host_name 两部分，使用 @ 连接。
此时如果查询用户表：
mysql> SELECT host,user,authentication_string FROM mysql.user; +-----------+------------------+------------------------------------------------------------------------+ | host | user | authentication_string | +-----------+------------------+------------------------------------------------------------------------+ | % | devp_role | | | % | read_role | | | % | write_role | | | localhost | dev01 | $A$005$lw58QcU;Q I|L`ktULChFhIVFxy5dsYrYmEhJkJqko4mezqefUFyT0zgyE2 | | localhost | mysql.infoschema | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED | | localhost | mysql.session | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED | | localhost | mysql.sys | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED | | localhost | root | $A$005$k D qbW(q*0Uev;TyKgUe56D9KXiFzPtrSGVxKjvM23CYN5pgE9dLrO0eT8 | +-----------+------------------+------------------------------------------------------------------------+ 8 rows in set (0.00 sec)
可以看出，角色实际上也是一个用户，但是没有密码。
5.3.2 为角色授权
为角色授权和用户授权类似，也是使用 GRANT 语句。我们分别为上面的 3 个角色分配权限：
mysql> GRANT ALL ON world.* TO devp_role; Query OK, 0 rows affected (0.01 sec) mysql> GRANT SELECT ON world.* TO read_role; Query OK, 0 rows affected (0.01 sec) mysql> GRANT INSERT, UPDATE, DELETE ON world.* TO write_role; Query OK, 0 rows affected (0.01 sec)
查看角色的权限和查询用户的权限类似：
mysql> SHOW GRANTS FOR devp_role; +------------------------------------------------------+ | Grants for devp_role@% | +------------------------------------------------------+ | GRANT USAGE ON *.* TO `devp_role`@`%` | | GRANT ALL PRIVILEGES ON `world`.* TO `devp_role`@`%` | +------------------------------------------------------+ 2 rows in set (0.00 sec)
5.3.2 为用户指定角色
接下来我们创建几个用户，然后为他们分别指定角色。
mysql> CREATE USER devp1 IDENTIFIED BY 'Devp1@2019'; Query OK, 0 rows affected (0.01 sec) mysql> CREATE USER read1 IDENTIFIED BY 'Read1@2019'; Query OK, 0 rows affected (0.01 sec) mysql> CREATE USER test1 IDENTIFIED BY 'Test1@2019'; Query OK, 0 rows affected (0.04 sec)
为用户指定角色和授予权限类似，也是使用GRANT语句：
mysql> GRANT devp_role TO devp1; Query OK, 0 rows affected (0.01 sec) mysql> GRANT read_role TO read1; Query OK, 0 rows affected (0.01 sec) mysql> GRANT read_role, write_role TO test1; Query OK, 0 rows affected (0.01 sec)
再次查询用户的权限：
mysql> SHOW GRANTS FOR devp1; +--------------------------------------+ | Grants for devp1@% | +--------------------------------------+ | GRANT USAGE ON *.* TO `devp1`@`%` | | GRANT `devp_role`@`%` TO `devp1`@`%` | +--------------------------------------+ 2 rows in set (0.00 sec)
如果想要知道用户通过角色获得的具体权限，可以使用USING选项：
mysql> SHOW GRANTS FOR devp1 USING devp_role; +--------------------------------------------------+ | Grants for devp1@% | +--------------------------------------------------+ | GRANT USAGE ON *.* TO `devp1`@`%` | | GRANT ALL PRIVILEGES ON `world`.* TO `devp1`@`%` | | GRANT `devp_role`@`%` TO `devp1`@`%` | +--------------------------------------------------+ 3 rows in set (0.00 sec)
另外，也可以通过将一个用户授予另一个用户，实现权限的复制：
mysql> GRANT read1 TO test1; Query OK, 0 rows affected (0.09 sec)
用户是具有登录权限的角色，角色是不能登录的用户。
5.3.4 设置默认角色
使用 devp1 连接数据库：
"C:\Program Files\MySQL\MySQL Server 8.0\bin\mysql.exe" -u devp1 -p Enter password: ********** Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 14 Server version: 8.0.17 MySQL Community Server - GPL Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> use world; ERROR 1044 (42000): Access denied for user 'devp1'@'%' to database 'world'
我们已经为用户 devp1 授予了 devp_role 角色，该角色拥有数据库 world 上的所有权限；错误的原因在于该角色没有自动激活。使用CURRENT_ROLE()函数查看当前启动的角色：
mysql> SELECT current_role(); +----------------+ | current_role() | +----------------+ | NONE | +----------------+ 1 row in set (0.00 sec)
结果显示没有任何角色。SET DEFAULT ROLE命令可以设置用户默认的活动角色：
mysql> SET DEFAULT ROLE ALL
-> TO devp1;
Query OK, 0 rows affected (0.01 sec)再次使用 devp1 连接数据库后，将会激活该用户所有的角色：
"C:\Program Files\MySQL\MySQL Server 8.0\bin\mysql.exe" -u devp1 -p Enter password: ********** Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 15 Server version: 8.0.17 MySQL Community Server - GPL Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. mysql> SELECT current_role(); +-----------------+ | current_role() | +-----------------+ | `devp_role`@`%` | +-----------------+ 1 row in set (0.00 sec) mysql> use world; Database changed mysql> select * from city limit 1; +----+-------+-------------+----------+------------+ | ID | Name | CountryCode | District | Population | +----+-------+-------------+----------+------------+ | 1 | Kabul | AFG | Kabol | 1780000 | +----+-------+-------------+----------+------------+ 1 row in set (0.00 sec)
另一种方式就是使用SET ROLE命令设置当前会话的活动角色：
SET ROLE NONE; SET ROLE ALL; SET ROLE DEFAULT;
以上语句分别表示不设置任何角色、设置所有角色以及设置默认的角色。
5.3.5 撤销角色的权限
撤销角色的权限与撤销用户的权限类似，撤销角色的权限同时会影响到具有该角色的用户。
以下语句撤销角色 write_role 的 DELETE 权限：
mysql> REVOKE DELETE
-> ON world.*
-> FROM write_role;
Query OK, 0 rows affected (0.14 sec)此时，用户 test1 上的相应权限也被撤销。
5.3.6 删除角色
DROP ROLE语句可以删除角色：
DROP ROLE role_name, ...;
删除角色的同时会撤销为用户指定的角色。以下语句将会删除角色 read_role 和 write_role：
mysql> DROP ROLE read_role, write_role; Query OK, 0 rows affected (0.10 sec)
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