SQL Server查询 - 查找最后的订单数据

Question

我有历史记录（没有正在进行的月份数据）表T1：

* na - 客户取消的服务

当前（201706）表T2（有持续月份的数据）：

如何编写Microsoft SQL Server查询以查找客户aaaa当前服务的最新订单日期？

答案：aaaa在201706订购了2，在201705订购了bbb - 1.

Answer 1

SELECT customer,service from T1 
GROUP BY customer,service HAVING service >=1 
ORDER BY ordered DESC

Answer 2

我建议每位客户只检索一个日期：

SELECT
latest_date.Customer as Customer,
T1.Service as Service
FROM
    (SELECT 
        Customer as Customer,
        max(Ordered) as date
    FROM T1 GROUP BY Customer) latest_date
    LEFT JOIN T1
        ON  latest_date.date=T1.ordered
GROUP BY Customer,Service