Show the ids for all employees.
select employee_id from employees
Also show their role names.
select t1.employee_id, t2.role_name from employees as t1 join roles as t2 on t1.role_code = t2.role_code
Which employees have "Human Resources" as their role?
select t1.employee_id from employees as t1 join roles as t2 on t1.role_code = t2.role_code where t2.role_name = "Human Resource"
Also show the employee ids with the role "Manager".
select t1.employee_id from employees as t1 join roles as t2 on t1.role_code = t2.role_code where t2.role_name = "Human Resource" or t2.role_name = "Manager"