ค้นหารายชื่อเมืองที่ไม่มีลูกค้าอาศัยอยู่
Find the list of cities that no customer is living in.
df_customers = pd.DataFrame(columns=['customer_id']); df_addresses = pd.DataFrame(columns=['city', 'address_id']); df_customer_addresses = pd.DataFrame(columns=['customer_id', 'address_id'])
df_addresses[~df_addresses['city'].isin(df_customer_addresses[df_customer_addresses['customer_id'].isin(df_customers['customer_id'])]['city'])]