create user test_user@localhost;
create role test_role1;
create role test_role2;
grant test_role1 to test_user@localhost;
grant test_role2 to test_role1;
select user, host from mysql.user where user not like 'root';
User	Host
mariadb.sys	localhost
test_role1	
test_role2	
test_user	localhost
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
	test_role1	test_role2	N
localhost	root	test_role1	Y
localhost	root	test_role2	Y
localhost	test_user	test_role1	N
grant select on mysql.roles_mapping to test_role2;
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
show grants;
Grants for test_user@localhost
GRANT USAGE ON *.* TO `test_user`@`localhost`
GRANT `test_role1` TO `test_user`@`localhost`
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	NULL
set role test_role1;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	test_role1
show grants;
Grants for test_user@localhost
GRANT SELECT ON `mysql`.`roles_mapping` TO `test_role2`
GRANT USAGE ON *.* TO `test_role1`
GRANT USAGE ON *.* TO `test_role2`
GRANT USAGE ON *.* TO `test_user`@`localhost`
GRANT `test_role1` TO `test_user`@`localhost`
GRANT `test_role2` TO `test_role1`
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
	test_role1	test_role2	N
localhost	root	test_role1	Y
localhost	root	test_role2	Y
localhost	test_user	test_role1	N
show grants;
Grants for test_user@localhost
GRANT SELECT ON `mysql`.`roles_mapping` TO `test_role2`
GRANT USAGE ON *.* TO `test_role1`
GRANT USAGE ON *.* TO `test_role2`
GRANT USAGE ON *.* TO `test_user`@`localhost`
GRANT `test_role1` TO `test_user`@`localhost`
GRANT `test_role2` TO `test_role1`
use mysql;
set role none;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	NULL
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
drop user 'test_user'@'localhost';
select * from mysql.tables_priv;
Host	Db	User	Table_name	Grantor	Timestamp	Table_priv	Column_priv
localhost	mysql	mariadb.sys	global_priv	root@localhost	0000-00-00 00:00:00	Select,Delete	
	mysql	test_role2	roles_mapping	root@localhost	0000-00-00 00:00:00	Select	
revoke select on mysql.roles_mapping from test_role2;
delete from mysql.user where user like'test_%';
delete from mysql.roles_mapping where Role like 'test%';
flush privileges;