Show the role code for all employees.
select role_code from employees
For each of them, count the number of employees.
select role_code, count(*) from employees group by role_code
Sort the codes by this count.
select role_code from employees group by role_code order by count(*) asc
Which code has the least?
select role_code from employees group by role_code order by count(*) asc limit 1