Question

I have one postgresql table where I store some stories from different sites.
At this table I got story_id and site_id fields.
Where story_id is the primary key and site_id is the id of the site where I got this story from.

I need to make SELECT from this table picking the latest 30 added stories.
But I dont want to get more than 2 stories comming from same site…

So if I have something like this:

story_id  | site_id
    1     |    1
    2     |    1
    3     |    2
    4     |    1
    5     |    3

My results must be : story_ids = 1,2,3,5!
4 must be skipped because I have already picked 2 ids with site_id 1.

Answer 1

select story_id,
       site_id 
from (
   select story_id,
          site_id,
          row_number() over (partition by site_id order by story_id desc) as rn
   from the_table
) t
where rn <= 2
order by story_id desc
limit 30

If you want more or less than 2 entries “per group” you have to adjust the value in the outer where clause.