Question: Find the name and gender of the staff who has been assigned the job of 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"