Database: department_store
Question: What are the names and genders of staff who have held the title Sales Person, but never Clerical Staff?
SQL: select t1.staff_name ,  t1.staff_gender from staff as t1 join staff_department_assignments as t2 on t1.staff_id  =  t2.staff_id where t2.job_title_code  =  "sales person" except select t1.staff_name ,  t1.staff_gender from staff as t1 join staff_department_assignments as t2 on t1.staff_id  =  t2.staff_id where t2.job_title_code  =  "clerical staff"