ค้นหานามสกุลของครูทุกคนที่สอน GELL TAMI
Find the last names of all the teachers that teach GELL TAMI.
df1 = pd.DataFrame(columns=['firstname', 'lastname', 'classroom']); df2 = pd.DataFrame(columns=['classroom', 'lastname'])
df2.loc[df2['classroom'].isin(df1.loc[(df1['firstname'] == 'GELL') & (df1['lastname'] == 'TAMI'), 'classroom']), 'lastname']