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
employees who can't authorize destruction of documents refers to finding employees not present in Destruction_Authorised_by_Employee_ID; sum(employee_id) is incorrect for counting employees; the correct approach should involve counting the number of unique employees not authorized for destruction.