从联合全部中获取具有最大日期的行答案

【问题标题】：Get Row with Max Date from a Union All从联合全部中获取具有最大日期的行
【发布时间】：2013-09-25 18:35:25
【问题描述】：

从下面的查询中，我想找到每个 request_id 的最后一个 activity_dt 的事件。我已经为此工作了几个小时，但无济于事。有人可以帮忙吗？

select a.event as event, a.activity_dt as activity_dt, b.request_id as request_id
from gs_pr_obl_event a, gs_pr_obl b
where a.obligation_id = b.obligation_id
union all
select event as event, activity_dt as activity_dt, request_id as request_id
from gs_pr_req_event;

【问题讨论】：

标签： oracle subquery max union

【解决方案1】：

这样试试，

SELECT event, MAX(activity_dt), request_id
FROM(
     SELECT A.event AS event, A.activity_dt AS activity_dt, b.request_id AS request_id
     FROM gs_pr_obl_event A, gs_pr_obl b
     WHERE A.obligation_id = b.obligation_id
     UNION ALL
     SELECT event AS event, activity_dt AS activity_dt, request_id AS request_id
     FROM gs_pr_req_event
     )
GROUP BY event, request_id;

【讨论】：