这是一个相当老的话题，但我想我要发表我的意见，就像公认的答案对我来说并不是特别有效一样。我在一个大型数据集上尝试了gbn的解决方案，发现它非常慢(在SQL Server 2012中500多万条记录上>45秒)。看一下执行计划，很明显问题在于它需要一个SORT操作，这会大大降低速度。

下面是我从实体框架中提取的一个替代方案，它不需要SORT操作，只进行非聚集索引搜索。这将在前面提到的记录集中将执行时间减少到< 2秒。

SELECT 
[Limit1].[DocumentID] AS [DocumentID], 
[Limit1].[Status] AS [Status], 
[Limit1].[DateCreated] AS [DateCreated]
FROM   (SELECT DISTINCT [Extent1].[DocumentID] AS [DocumentID] FROM [dbo].[DocumentStatusLogs] AS [Extent1]) AS [Distinct1]
OUTER APPLY  (SELECT TOP (1) [Project2].[ID] AS [ID], [Project2].[DocumentID] AS [DocumentID], [Project2].[Status] AS [Status], [Project2].[DateCreated] AS [DateCreated]
    FROM (SELECT 
        [Extent2].[ID] AS [ID], 
        [Extent2].[DocumentID] AS [DocumentID], 
        [Extent2].[Status] AS [Status], 
        [Extent2].[DateCreated] AS [DateCreated]
        FROM [dbo].[DocumentStatusLogs] AS [Extent2]
        WHERE ([Distinct1].[DocumentID] = [Extent2].[DocumentID])
    )  AS [Project2]
    ORDER BY [Project2].[ID] DESC) AS [Limit1]

Now I'm assuming something that isn't entirely specified in the original question, but if your table design is such that your ID column is an auto-increment ID, and the DateCreated is set to the current date with each insert, then even without running with my query above you could actually get a sizable performance boost to gbn's solution (about half the execution time) just from ordering on ID instead of ordering on DateCreated as this will provide an identical sort order and it's a faster sort.

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;

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]

我相信这是可以做到的。这可能需要一些调整，但你可以从组中选择最大值。

这些答案太夸张了。

SELECT
  d.DocumentID,
  MAX(d.Status),
  MAX(d1.DateCreated)
FROM DocumentStatusLogs d, DocumentStatusLogs d1
USING DocumentID
GROUP BY 1
ORDER BY 3 DESC

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…