Question

我有一个如下表

TestDetails

Submitted_on                      Subject    Submitted_By
3/4/2020 7:45:26 PM               English       Shyam
3/4/2020 9:45:26 PM               English       Rahul
3/5/2020 9:45:26 PM               Arabic        Rahul
3/4/2020 8:45:26 PM               French        Yash
3/4/2020 7:45:26 PM               Spanish       John
3/4/2020 6:45:26 PM               Spanish       John

我想从上表中为每个主题选择最新提交的内容。输出应为：

 Submitted_on                     Subject    Submitted_By
3/4/2020 9:45:26 PM               English       Rahul
3/5/2020 9:45:26 PM               Arabic        Rahul
3/4/2020 8:45:26 PM               French        Yash
3/4/2020 7:45:26 PM               Spanish       John

我尝试过如下但是将输出作为

 Submitted_on                    Subject    Submitted_By
3/4/2020 7:45:26 PM               English       Shyam
3/4/2020 9:45:26 PM               English       Rahul
3/5/2020 9:45:26 PM               Arabic        Rahul
3/4/2020 8:45:26 PM               French        Yash
3/4/2020 7:45:26 PM               Spanish       John


SELECT MAX(Submitted_on),Subject,Submitted_By FROM TestDetails GROUP BY Subject,Submitted_By

Answer 1

使用过滤。这是一种方法：

select td.*
from testdetails td
where td.Submitted_on = (select max(td2.Submitted_on)
                         from testdetails td2
                         where td2.subject = td.subject
                        );

要获得更大数据集的性能，您需要在testdetails(subject, submitted_on)上建立索引。

Answer 2

找到以下查询

;WITH CTE AS
(
    SELECT ROW_NUMBER() OVER (PARTITION BY subject ORDER BY subject DESC) duplicates, * 
    FROM TestDetails
)
SELECT submitted_on, subject, submitted_by FROM CTE WHERE duplicates = 1

分组依据的SQL查询作为内部查询

2 个答案: