select t1.order_id,t1.customer_name,t1.order_date
from(
select orders.order_id ,customers.customer_name, 
orders.order_date,rank() over(partition by orders.customer_id 
order by orders.order_date desc) as paiming   
from orders
left join customers
using(customer_id)
) t1
where t1.paiming=1
;

开窗函数秒了