Question

I have a table with actions performed by actors and want to return 10 of the most recent actions. I want actors to be unique within this list. ‘created’ is a time/date stamp. How can I do this most efficiently? I came up with the following query, which works:

SELECT * 
FROM activities a
JOIN 
(SELECT actor, MAX(created) created 
 FROM activities 
 WHERE comment_type <> 'profile.status' 
 GROUP BY actor) t ON (a.actor = t.actor AND a.created = t.created) LIMIT 10

The table could eventually be quite large.

Answer 1

You could put the limit 10 inside the subquery.
Other than that it looks OK

SELECT * FROM activities a
INNER JOIN (
            SELECT 
              actor
              , MAX(created) created 
            FROM activities 
            WHERE comment_type <> 'profile.status' 
            GROUP BY actor
            LIMIT 10 OFFSET 0) t
      ON (a.actor = t.actor AND a.created = t.created) LIMIT 10