SHOW GRANTS FOR root@invalid_host;
ERROR 42000: There is no such grant defined for user 'root' on host 'invalid_host'
create user test;
create user foo;
create role foo;
grant foo to test;
connect  conn_1, localhost, test,,;
set role foo;
show grants for test;
Grants for test@%
GRANT foo TO 'test'@'%'
GRANT USAGE ON *.* TO 'test'@'%'
show grants for foo;
Grants for foo
GRANT USAGE ON *.* TO 'foo'
show grants for foo@'%';
ERROR 42000: Access denied for user 'test'@'%' to database 'mysql'
connection default;
drop user test, foo;
drop role foo;