create user 'test_user'@'localhost';
create role test_role1;
grant test_role1 to test_user@localhost;
select user, host from mysql.user where user not like 'root';
User	Host
mariadb.sys	localhost
test_role1	
test_user	localhost
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
localhost	root	test_role1	Y
localhost	test_user	test_role1	N
grant select on mysql.* to test_role1;
grant insert, delete on mysql.roles_mapping to test_role1;
grant reload on *.* to test_role1;
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
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
select * from mysql.roles_mapping;
Host	User	Role	Admin_option
localhost	root	test_role1	Y
localhost	test_user	test_role1	N
insert into mysql.user (user, host) values ('Dummy', 'Dummy');
ERROR 42000: INSERT command denied to user 'test_user'@'localhost' for table `mysql`.`user`
insert into mysql.roles_mapping values ('localhost', 'test_user', 'test_role2', 'N');
delete from mysql.roles_mapping where Role='test_role2';
use mysql;
set role none;
select current_user(), current_role();
current_user()	current_role()
test_user@localhost	NULL
use mysql;
ERROR 42000: Access denied for user 'test_user'@'localhost' to database 'mysql'
select * from mysql.roles_mapping;
ERROR 42000: SELECT command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
insert into mysql.user (user, host) values ('Dummy', 'Dummy');
ERROR 42000: INSERT command denied to user 'test_user'@'localhost' for table `mysql`.`user`
insert into mysql.roles_mapping values ('localhost', 'test_user', 'test_role2', 'N');
ERROR 42000: INSERT command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
delete from mysql.roles_mapping where Role='test_role2';
ERROR 42000: DELETE command denied to user 'test_user'@'localhost' for table `mysql`.`roles_mapping`
drop user 'test_user'@'localhost';
revoke select on mysql.* from test_role1;
revoke insert, delete on mysql.roles_mapping from test_role1;
drop role test_role1;
delete from mysql.roles_mapping where Role='test_role1';
flush privileges;