List the name of staff who has been assigned multiple jobs.
create table staff (staff_name varchar, staff_id varchar, PRIMARY KEY (staff_name)); create table staff_department_assignments (staff_id varchar, PRIMARY KEY (staff_id))
select t1.staff_name from staff as t1 join staff_department_assignments as t2 on t1.staff_id = t2.staff_id group by t2.staff_id having count(*) > 1