What are all the employee ids?
select employee_id from employees
Also, what are the names of the countries that they work in?
select employee_id, country_name from employees as t1 join departments as t2 on t1.department_id = t2.department_id join locations as t3 on t2.location_id = t3.location_id join countries as t4 on t3.country_id = t4.country_id