What are the role codes?
select role_code from roles;
How about their corresponding role_description?
select role_code, role_description from roles;
List role description, role code and number of employees of each role?
select t1.role_description, t2.role_code, count(*) from roles as t1 join employees as t2 on t1.role_code = t2.role_code group by t2.role_code;