Show the information about all the staff department assignments.
select * from staff_department_assignments
When was the latest department assignment of Clerical Staff?
select max(date_assigned_to) from staff_department_assignments where job_title_code = 'Clerical Staff'
What is id of the staff who had a Staff Department Assignment earlier than this date?
select staff_id from staff_department_assignments where date_assigned_to < (select max(date_assigned_to) from staff_department_assignments where job_title_code = 'Clerical Staff')