如何从数据库表中的重复行中选择具有最新时间戳的行？

Question

我有一个包含重复行和三行的表 - 如何选择重复但具有最新时间戳以及未加工行的行？

 -------------------------------------
| pk_id | user_id | some_timestamp    |
|-------------------------------------|
| 1     | 123     | 10-Jun-12 14.30   |
| 2     | 123     | 19-Jun-12 21.50   |
| 3     | 567     | 10-Jun-12 09.23   |
| 4     | 567     | 12-Jun-12 09.45   |
| 5     | 567     | 13-Jun-12 08.40   |
| 6     | 890     | 13-Jun-12 08.44   |
 -------------------------------------

所以我最终得到:

 -------------------------------------
| pk_id | user_id | some_timestamp    |
|-------------------------------------|
| 2     | 123     | 19-Jun-12 21.50   |
| 5     | 567     | 13-Jun-12 08.40   |
| 6     | 890     | 13-Jun-12 08.44   |
 -------------------------------------

Answer 1

SELECT * FROM ( 
SELECT pk_id, 
       user_id, 
       some_timestamp, 
       ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY some_timestamp DESC) col 
FROM table) x  
WHERE x.col = 1