/*确保每个用户最新订单只有一个，两个条件一起约束*/
select order_id
,customer_name
,order_date
from orders o
join customers c on o.customer_id = c.customer_id
where (o.customer_id,o.order_id) in(
select o.customer_id
,max(order_id) over(partition by o.customer_id) as order_id
from orders o
)
order by customer_name