试试这个:

SELECT [DocumentID]
    ,[tmpRez].value('/x[2]', 'varchar(20)') AS [Status]
    ,[tmpRez].value('/x[3]', 'datetime') AS [DateCreated]
FROM (
    SELECT [DocumentID]
        ,cast('<x>' + max(cast([ID] AS VARCHAR(10)) + '</x><x>' + [Status] + '</x><x>' + cast([DateCreated] AS VARCHAR(20))) + '</x>' AS XML) AS [tmpRez]
    FROM DocumentStatusLogs
    GROUP BY DocumentID
    ) AS [tmpQry]

;WITH cte AS
(
   SELECT *,
         ROW_NUMBER() OVER (PARTITION BY DocumentID ORDER BY DateCreated DESC) AS rn
   FROM DocumentStatusLogs
)
SELECT *
FROM cte
WHERE rn = 1

如果您希望每天有2个条目，那么这将任意选择一个。要获得一天的两个条目，请使用DENSE_RANK代替

至于是否正常化，这取决于你是否想:

在两个地方保持状态 保存状态历史 .．.

目前，您保留了状态历史。如果你也想在父表中保持最新状态(这是非规范化的)，你需要一个触发器来维持父表中的“状态”。或者删除这个状态历史表。

I've done some timings over the various recommendations here, and the results really depend on the size of the table involved, but the most consistent solution is using the CROSS APPLY These tests were run against SQL Server 2008-R2, using a table with 6,500 records, and another (identical schema) with 137 million records. The columns being queried are part of the primary key on the table, and the table width is very small (about 30 bytes). The times are reported by SQL Server from the actual execution plan.

Query                                  Time for 6500 (ms)    Time for 137M(ms)

CROSS APPLY                                    17.9                17.9
SELECT WHERE col = (SELECT MAX(COL)…)           6.6               854.4
DENSE_RANK() OVER PARTITION                     6.6               907.1

我认为真正令人惊讶的是，无论涉及的行数是多少，CROSS APPLY的时间都是如此一致。

一些数据库引擎*开始支持允许过滤窗口函数结果的qualifier子句(接受的答案使用该子句)。

所以公认的答案可以变成

SELECT *, ROW_NUMBER() OVER (PARTITION BY DocumentID ORDER BY DateCreated DESC) AS rn
FROM DocumentStatusLogs
QUALIFY rn = 1

查看这篇文章以获得更深入的解释:https://jrandrews.net/the-joy-of-qualify

您可以使用此工具查看哪个数据库支持此子句:https://www.jooq.org/translate/ 当目标方言不支持qualifier子句时，可以选择转换它。

*Teradata, BigQuery, H2, Snowflake…

此解决方案可用于获取每个分区的TOP N最近行(在本例中，WHERE语句中的N为1,partition为doc_id):

SELECT T.doc_id, T.status, T.date_created FROM 
(
    SELECT a.*, ROW_NUMBER() OVER (PARTITION BY doc_id ORDER BY date_created DESC) AS rnk FROM doc a
) T
WHERE T.rnk = 1;

SELECT documentid, 
       status, 
       datecreated 
FROM   documentstatuslogs dlogs 
WHERE  status = (SELECT status 
                 FROM   documentstatuslogs 
                 WHERE  documentid = dlogs.documentid 
                 ORDER  BY datecreated DESC 
                 LIMIT  1)