How many employees are there?
select count ( employee_id ) from employees
How many employee have the ability to authorize the destruction of documents?
select count ( destruction_authorised_by_employee_id ) from documents_to_be_destroyed
What are the ids of those particular employees?
select destruction_authorised_by_employee_id from documents_to_be_destroyed
Now how many employees can't authorize the destruction of documents.
select sum ( employee_id ) from employees except select destruction_authorised_by_employee_id from documents_to_be_destroyed
May I have the ids of those employees who cant authorize the destruction of documents?
select employee_id from employees except select destruction_authorised_by_employee_id from documents_to_be_destroyed