ค้นหาชื่อลูกค้าที่ไม่เคยสั่งซื้อ
Find the names of customers who never placed an order.
df_customers = pd.DataFrame(columns=['customer_name', 'customer_id']); df_customer_orders = pd.DataFrame(columns=['customer_id'])
list(set(df_customers['customer_name']) - set(df_customers[df_customers['customer_id'].isin(df_customer_orders['customer_id'])]['customer_name']))