create user ''@localhost;

create user c;

grant select on mysql.* to c;

create role r1;

grant r1 to c;

connect (c,localhost,c,,,,,);

select user(), current_user();

--error ER_TABLEACCESS_DENIED_ERROR

select user from mysql.user group by user;

set role r1;

disconnect c;

connection default;

drop role r1;

drop user c;

drop user ''@localhost;