What are all the users that have logged in?
select * from users where user_login = 1
Among those users, which role is the most popular one?
select role_code from users where user_login = 1 group by role_code order by count(*) desc limit 1
Show the description of that role.
select role_description from roles where role_code = (select role_code from users where user_login = 1 group by role_code order by count(*) desc limit 1)