SET DEFAULT ROLE
This statement sets a specific role to be applied to a user by default. Thus, they will automatically have the permissions associated with a role without having to execute SET ROLE <rolename> or SET ROLE ALL.
Synopsis
SetDefaultRoleStmt:

SetDefaultRoleOpt:

RolenameList:

UsernameList:

Examples
Connect to TiDB as the root user:
mysql -h 127.0.0.1 -P 4000 -u root
Create a new role analyticsteam and a new user 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)
Connect to TiDB as the jennifer user:
mysql -h 127.0.0.1 -P 4000 -u jennifer
Note that by default jennifer needs to execute SET ROLE analyticsteam in order to be able to use the privileges associated with the analyticsteam role:
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)
Connect to TiDB as the root user:
mysql -h 127.0.0.1 -P 4000 -u root
The statement SET DEFAULT ROLE can be used to associate the role analyticsteam to jennifer:
SET DEFAULT ROLE analyticsteam TO jennifer;
Query OK, 0 rows affected (0.02 sec)
Connect to TiDB as the jennifer user:
mysql -h 127.0.0.1 -P 4000 -u jennifer
After this, the user jennifer has the privileges associated with the role analyticsteam and jennifer does not have to execute the statement SET ROLE:
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 will not automatically GRANT the associated role to the user. Attempting to SET DEFAULT ROLE for a role that jennifer does not have granted results in the following error:
SET DEFAULT ROLE analyticsteam TO jennifer;
ERROR 3530 (HY000): `analyticsteam`@`%` is is not granted to jennifer@%
MySQL compatibility
This statement is understood to be fully compatible with roles, which are a feature of MySQL 8.0. Any compatibility differences should be reported via an issue on GitHub.