Show the ids of the employees who don't authorize destruction for any document.
create table documents_to_be_destroyed (employee_id varchar, destruction_authorised_by_employee_id varchar, PRIMARY KEY (employee_id)); create table employees (employee_id varchar, destruction_authorised_by_employee_id varchar, PRIMARY KEY (employee_id))
select employee_id from employees except select destruction_authorised_by_employee_id from documents_to_be_destroyed