Show all employee names.
select employee_name from employees
What are the names of the employees who authorized document destruction.
select t2.employee_name from documents_to_be_destroyed as t1 join employees as t2 on t1.destruction_authorised_by_employee_id = t2.employee_id
Also show the names for those who destroyed the corresponding documents.
select t2.employee_name, t3.employee_name from documents_to_be_destroyed as t1 join employees as t2 on t1.destruction_authorised_by_employee_id = t2.employee_id join employees as t3 on t1.destroyed_by_employee_id = t3.employee_id