Give the id and name of the staff who has been assigned for the shortest period?
SELECT T1.staff_id ,  T1.staff_name FROM staff AS T1 JOIN Staff_Department_Assignments AS T2 ON T1.staff_id   =   T2.staff_id ORDER BY date_assigned_to - date_assigned_from LIMIT 1
shortest period refers to MIN(date_assigned_to - date_assigned_from);