题解 | 查询订单

select
    a.order_id,
    c.customer_name,
    a.order_date
from
    orders a 
inner join
    (select
        customer_id,
        max(order_date) as order_date
    from
        orders
    group by 
        customer_id) b on a.customer_id = b.customer_id and a.order_date = b.order_date
left join
    customers c on a.customer_id = c.customer_id
order by 
    2