Logic Solution
select employee_id from employees  where employee_id not in(select employee_id from salaries)\nunion\nselect employee_id from salaries where employee_id not in 
select employee_id from employees  where employee_id not in(select employee_id from salaries)\nunion\nselect employee_id from salaries where employee_id not in (select employee_id from employees)
['Union Find', 'Oracle']