อาจารย์ภาควิชาประวัติศาสตร์ที่ไม่ได้สอนในชั้นเรียนมีชื่ออะไร
What is the first names of the professors from the history department who do not teach a class.
df_professor = pd.DataFrame(columns=['emp_num', 'dept_code']); df_department = pd.DataFrame(columns=['dept_code', 'dept_name']); df_class = pd.DataFrame(columns=['prof_num']); df_employee = pd.DataFrame(columns=['emp_fname', 'emp_num'])
set(df_employee[(df_employee['emp_num'].isin(df_professor[df_professor['dept_code'].isin(df_department[df_department['dept_name'] == 'History']['dept_code'])]['emp_num']))]['emp_fname']) - set(df_employee[df_employee['emp_num'].isin(df_class['prof_num'])]['emp_fname'])