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sql - SQL获取分组的最大日期

问题描述

我有一个像这样的事务表......

-------------------------------------------------------------------------------------
Subject_id | Question_id | Answerd_id | Student_id | Answer_text | Insert_DTM
-------------------------------------------------------------------------------------
5005       | 3004        | 1004       | 1309       | test        | 2018-05-31 12:07:42
-------------------------------------------------------------------------------------
5005       | 3005        | 1005       | 1309       | test        | 2018-05-31 12:07:42
-------------------------------------------------------------------------------------
5005       | 3004        | NULL       | 1309       | Null        | 2018-05-31 12:09:43
-------------------------------------------------------------------------------------
5005       | 3002        | NULL       | 1309       | Null        | 2018-05-31 12:07:42
-------------------------------------------------------------------------------------
5005       | 3005        | 1005       | 1309       | test        | 2018-05-31 11:35:47
-------------------------------------------------------------------------------------
5005       | 3005        | 1005       | 1309       |             |2018-05-31 11:36:37

从这个表中，我必须找出学生和学科 ID 的最新回答行。

我正在使用的 SQL ..

SELECT subject_id, 
       question_id, 
       answer_id, 
       student_id, 
       answer_text, 
       insert_dtm 
FROM   exam_trans 
WHERE  student_id = 1309 
       AND subject_id = 5005 
       AND insert_dtm IN (SELECT Max(insert_dtm) 
                          FROM   exam_trans 
                          WHERE  student_id = 1309 
                                 AND subject_id = 5005 
                          GROUP  BY question_id) 
GROUP  BY subject_id, 
          question_id, 
          answer_id, 
          member_id, 
          answer_text, 
          insert_dtm 
ORDER  BY answer_id, 
          question_id DESC

但作为输出我得到

-------------------------------------------------------------------------------------
Subject_id | Question_id | Answerd_id | Student_id | Answer_text | Insert_DTM
-------------------------------------------------------------------------------------
5005       | 3004        | 1004       | 1309       | test        | 2018-05-31 12:07:42
-------------------------------------------------------------------------------------
5005       | 3005        | 1005       | 1309       | test        | 2018-05-31 12:07:42
---------------------------------------------------------------------------------------
5005       | 3004        | NULL       | 1309       | Null        | 2018-05-31 12:09:43
--------------------------------------------------------------------------------------
5005       | 3002        | NULL       | 1309       | Null        | 2018-05-31 12:07:42

3004 在输出中出现两次，但我的预期输出是

Subject_id | Question_id | Answerd_id | Student_id | Answer_text | Insert_DTM
-------------------------------------------------------------------------------------
5005       | 3005        | 1005       | 1309       | test        | 2018-05-31 12:07:42
---------------------------------------------------------------------------------------
5005       | 3004        | NULL       | 1309       | Null        | 2018-05-31 12:09:43
--------------------------------------------------------------------------------------
5005       | 3002        | NULL       | 1309       | Null        | 2018-05-31 12:07:42

3004 应该只用最近的时间戳来一次....

任何人都可以帮助我使用正确的 SQL...

我在 AWS 中使用 Oracle RDS

标签： sqloracleoracle11gamazon-rds

解决方案

因为这是更好的用途ROW_NUMBER()

SELECT *
FROM (SELECT *,
             ROW_NUMBER() OVER (PARTION BY Question_id, Subject_id
                                ORDER BY Insert_DTM DESC) as rn
      FROM exam_trans 
      WHERE  student_id = 1309 
        AND  subject_id = 5005 
     )
WHERE rn = 1

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