在 DB2/400 中获取仅按用户分组的最新结果答案

【问题标题】：Getting latest of many results only grouped by user in DB2/400在 DB2/400 中获取仅按用户分组的最新结果
【发布时间】：2019-10-07 18:29:42
【问题描述】：

我正在发布我的查询和结果，但我试图将其限制为仅由创建者提供的最新状态和时间戳。

    select t2.creator, t1.event_id, t2.status, max(t2.createdTS)
    from schema.event T1
    inner join schema.event_to_event_statust T2
    on t1.event_id = t2.event_id
    group by t2.creator, t1.event_id, t2.status;



    creator     |   event_id    |   status  | createdTS
    -----------------------------------------------------
    123                 1           New         2019-01-29 17:27:50.899408
    123                 1           Live        2019-01-29 17:29:50.899408
    123                 1           Closed      2019-01-29 17:45:50.899408
    456                 5           New         2019-01-29 17:32:50.899408
    456                 5           Live        2019-01-29 17:48:50.899408

我想要的这组结果实际上是

    creator     |   event_id    |   status  | createdTS
    -----------------------------------------------------
    123                 1           Closed      2019-01-29 17:45:50.899408
    456                 5           Live        2019-01-29 17:48:50.899408

所以我应该每个创作者只有一行，它应该是最新的记录。我做错了什么？

【问题讨论】：

另外，我的问题在没有评论/解释的情况下被否决，但无论如何。
真的需要加入吗？
是的，这是我获取用户状态的唯一方法
状态从t2中选择

标签： sql db2 db2-400

【解决方案1】：

以下是否在您的 IBM i 上“按原样”工作？

WITH RES (creator, event_id, status, createdTS) AS 
(
VALUES
  (123, 1, 'New',    TIMESTAMP('2019-01-29 17:27:50.899408'))
, (123, 1, 'Live',   TIMESTAMP('2019-01-29 17:29:50.899408'))
, (123, 1, 'Closed', TIMESTAMP('2019-01-29 17:45:50.899408'))
, (456, 5, 'New',    TIMESTAMP('2019-01-29 17:32:50.899408'))
, (456, 5, 'Live',   TIMESTAMP('2019-01-29 17:48:50.899408'))
)
SELECT creator, event_id, status, createdTS
FROM 
(
SELECT creator, event_id, status, createdTS
, ROWNUMBER() OVER (PARTITION BY creator ORDER BY createdTS desc) AS rn
FROM RES
) T
WHERE RN=1;

如果不是，那么您的 IBM i 版本和修改是什么？

【讨论】：

【解决方案2】：

试试

with temp as (
 select t2.creator, t1.event_id, t2.status, t2.createdTS
        row_number() over (partition by t2.creator order by t2.createdTS desc) as rownum
    from schema.event T1
    inner join schema.event_to_event_statust T2
    on t1.event_id = t2.event_id
    group by t2.creator, t1.event_id, t2.status
)
select creator, event_id, status, createdTS
  from temp
 where rownum = 1

@MarkBarinstein：感谢 SQL 更正

另一种可能是

select t2.creator, t1.event_id, t2.status, t2.createdTS
    from event T1
    inner join event_to_event_status T2
    on t1.event_id = t2.event_id
 INNER JOIN (select event_id, creator, max(createdts) AS createdts
              FROM  event_to_event_status
              GROUP BY event_id, creator) AS x
              ON t2.event_id = x.event_id AND t2.creator = x.creator AND t2.createdts = x.createdts

抱歉，我没有 iSeries 可以试用

【讨论】：

好的，所以我必须修复它以将 row_number 用于我的带有 iseries 7 的 db2 版本，但我仍然得到 Token PARTITION was not valid, valid tokens:)