为评估为真的 IN 条件元素设置限制

Question

table: t
+--------------+-----------+-----------+
| Id           | price     | Date      |
+--------------+-----------+-----------+
|  1           | 30        | 2021-05-09|
|  1           | 24        | 2021-04-26|
|  1           | 33        | 2021-04-13|
|  2           | 36        | 2021-04-18|
|  3           | 15        | 2021-04-04| 
|  3           | 33        | 2021-05-06|
|  4           | 46        | 2021-02-16|
+--------------+-----------+-----------+

I want to select rows where id is 1,2,4 and get maximum 2 row for each id by date descending order.

+--------------+-----------+-----------+
| Id           | price     | Date      |
+--------------+-----------+-----------+
|  1           | 30        | 2021-05-09|
|  1           | 24        | 2021-04-26|
|  2           | 36        | 2021-04-18|
|  4           | 46        | 2021-02-16|
+--------------+-----------+-----------+

Something like:

Select * from t where Id IN ('1','2','4') limit 2 order by Date desc; 

this will limit the overall result fetched.

Answer 1

Use row_number() :

select id, price, date
from (select t.*,
             row_number() over (partition by id order by date desc) as seqnum
      from t
      where id in (1, 2, 4)
     ) t
where seqnum <= 2;

Probably the most efficient method is a correlated subquery:

select t.*
from t
where t.id in (1, 2, 4) and
      t.date >= coalesce( (select t2.date
                           from t t2
                           where t2.id = t.id
                           order by t2.date desc
                           limit 1,1
                           ), t.date
                        );

For performance, you want an index on (id, date) . Also, this can return duplicates if there are multiple rows for a given id on the same date.

Here is a db<>fiddle.