从每个类别中获取最后五条记录

Question

I have 2 tables in mySQL database

First table is tbl_article_category which has article_category_id as primary key and the second tbl_article and it has article_id as primary and article_category_id as foreign key

now I want to get the last Five recode form each category so if i have 5 categories i want to get 25 recodes last five from each one

do you have any thought to get this recodes

Answer 1

You can try this query -

SELECT * FROM (
  SELECT a1.*, COUNT(*) cnt FROM tbl_article a1
  LEFT JOIN tbl_article a2
    ON a1.article_category_id = a2.article_category_id AND a2.article_id <= a1.article_id
  GROUP BY
    a1.article_category_id, c1.article_id
) t
WHERE cnt <= 5;

It finds last records using article_id values, but you may sort records using any field you need, eg by DATETIME field.

Answer 2

Here is an amusing/kludgy way to do this:

select ac.category_id, a.*
from (select category_id,
             substring_index(group_concat(ac.article_id order by ac.article_category_id desc),
                             ',', 5) as last5
      from tbl_article_category ac
      group by category_id
     ) c5 join
     article a
     on find_in_set(a.article_id, last5) > 0
order by 1;

Note: this does not have performance in mind. In particular, the join cannot take advantage of indexes. But, for 25 rows, the performance should be fine.