Question: What is 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"