SET DEFAULT ROLE
此语句用于将特定角色设置为默认应用于某个用户。因此，该用户在登录后会自动拥有与该角色相关联的权限，无需执行 SET ROLE <rolename> 或 SET ROLE ALL。
概要
- SetDefaultRoleStmt
SetDefaultRoleStmt ::=
"SET" "DEFAULT" "ROLE" ( "NONE" | "ALL" | Rolename ("," Rolename)* ) "TO" Username ("," Username)*
示例
以 root 用户连接到 TiDB：
mysql -h 127.0.0.1 -P 4000 -u root
创建一个新角色 analyticsteam 和一个新用户 jennifer：
CREATE ROLE analyticsteam;
Query OK, 0 rows affected (0.02 sec)
GRANT SELECT ON test.* TO analyticsteam;
Query OK, 0 rows affected (0.02 sec)
CREATE USER jennifer;
Query OK, 0 rows affected (0.01 sec)
GRANT analyticsteam TO jennifer;
Query OK, 0 rows affected (0.01 sec)
以 jennifer 用户连接到 TiDB：
mysql -h 127.0.0.1 -P 4000 -u jennifer
注意，默认情况下，jennifer 需要执行 SET ROLE analyticsteam 才能使用与 analyticsteam 角色相关联的权限：
SHOW GRANTS;
+---------------------------------------------+
| Grants for User |
+---------------------------------------------+
| GRANT USAGE ON *.* TO 'jennifer'@'%' |
| GRANT 'analyticsteam'@'%' TO 'jennifer'@'%' |
+---------------------------------------------+
2 rows in set (0.00 sec)
SHOW TABLES in test;
ERROR 1044 (42000): Access denied for user 'jennifer'@'%' to database 'test'
SET ROLE analyticsteam;
Query OK, 0 rows affected (0.00 sec)
SHOW GRANTS;
+---------------------------------------------+
| Grants for User |
+---------------------------------------------+
| GRANT USAGE ON *.* TO 'jennifer'@'%' |
| GRANT Select ON test.* TO 'jennifer'@'%' |
| GRANT 'analyticsteam'@'%' TO 'jennifer'@'%' |
+---------------------------------------------+
3 rows in set (0.00 sec)
SHOW TABLES IN test;
+----------------+
| Tables_in_test |
+----------------+
| t1 |
+----------------+
1 row in set (0.00 sec)
以 root 用户连接到 TiDB：
mysql -h 127.0.0.1 -P 4000 -u root
SET DEFAULT ROLE 语句可以用来将 analyticsteam 角色关联到 jennifer：
SET DEFAULT ROLE analyticsteam TO jennifer;
Query OK, 0 rows affected (0.02 sec)
以 jennifer 用户连接到 TiDB：
mysql -h 127.0.0.1 -P 4000 -u jennifer
之后，jennifer 用户将拥有与 analyticsteam 角色相关联的权限，且无需执行 SET ROLE 语句：
SHOW GRANTS;
+---------------------------------------------+
| Grants for User |
+---------------------------------------------+
| GRANT USAGE ON *.* TO 'jennifer'@'%' |
| GRANT Select ON test.* TO 'jennifer'@'%' |
| GRANT 'analyticsteam'@'%' TO 'jennifer'@'%' |
+---------------------------------------------+
3 rows in set (0.00 sec)
SHOW TABLES IN test;
+----------------+
| Tables_in_test |
+----------------+
| t1 |
+----------------+
1 row in set (0.00 sec)
SET DEFAULT ROLE 不会自动 GRANT 相关角色给用户。尝试为 jennifer 未被授予的角色执行 SET DEFAULT ROLE 时，会出现以下错误：
SET DEFAULT ROLE analyticsteam TO jennifer;
ERROR 3530 (HY000): `analyticsteam`@`%` is is not granted to jennifer@%
MySQL 兼容性
TiDB 中的 SET DEFAULT ROLE 语句与 MySQL 8.0 中的角色功能完全兼容。如果发现任何兼容性差异，请报告一个 bug。