SQL-如何根据最大日期和GROUP BY获得结果

Question

I want to get a result for maximum created_at and for each application_id group. Below are the data sample,

application_id | checkpoint_id | created_at 
1              |  260          | 2018-12-28 11:54:52    
11             |  259          | 2018-12-24 18:16:30    
11             |  260          | 2018-12-26 17:48:58    
12             |  260          | 2018-12-26 17:48:58    
12             |  261          | 2018-12-26 18:00:00    

The result that I want is only for checkpoint_id = 260 . For example, the result above that I want is application_id no. 1 & 11.

The query that I tried,

SELECT * FROM histories h 
WHERE `checkpoint_id` = 260
AND created_at = (
  SELECT MAX(`created_at`)
  FROM histories
  GROUP BY h.application_id, h.checkpoint_id
)

Result

application_id | checkpoint_id | created_at 
1              |  260          | 2018-12-28 11:54:52      

I am expecting to get 2 rows for id no 1 and 11. Is there a way to do it.

Update on latest query

Just to update on my latest query that I achieved to get the expected results. The query is as below,

SELECT * FROM (
    SELECT application_id, checkpoint_id, created_at 
    FROM histories 
    GROUP BY application_id, checkpoint_id
) AS h 
WHERE h.checkpoint_id = 260 AND h.created_at=(
    SELECT MAX(`created_at`) 
    FROM histories h2 
    WHERE h2.application_id=h.application_id    
)

Answer 1

Use a correlated subquery:

SELECT h.*
FROM histories h 
WHERE h.checkpoint_id = 260 AND
      h.created_at = (SELECT MAX(h.created_at)
                      FROM histories h2
                      WHERE h2.application_id = h2.application_id AND
                            h2.checkpoint_id = h.checkpoint_id
                     );

Your version is just comparing each created_at to a created_at that is the maximum for any application/checkpoint combination. You want the one that is specifically for your combination.

Answer 2

My approach:

SELECT * 
FROM histories h 
WHERE h.checkpoint_id = 260
order by h.created_at desc
LIMIT 1