CREATE TABLE Employees (employee_id VARCHAR, Destruction_Authorised_by_Employee_ID VARCHAR)
CREATE TABLE Documents_to_be_destroyed (employee_id VARCHAR, Destruction_Authorised_by_Employee_ID VARCHAR)

Show the ids of the employees who don't authorize destruction for any document.
SELECT employee_id FROM Employees EXCEPT SELECT Destruction_Authorised_by_Employee_ID FROM Documents_to_be_destroyed
SELECT "employee_id" FROM "Employees" EXCEPT SELECT "Destruction_Authorised_by_Employee_ID" FROM "Documents_to_be_destroyed"