Question

MySQL 5.5 – in my table logs, how do I sum the values of the n most recent entries per user_id, for all user_ids?

CREATE  TABLE `logs` (
  `id` INT NOT NULL ,
  `user_id` INT NULL ,
  `value` INT NULL ,
  `date_created` DATETIME NULL ,
  PRIMARY KEY (`id`) );

Answer 1

Try this query:

SELECT   `user_id`, SUM(`value`)
FROM     logs` as l
WHERE    (SELECT COUNT(*)
          FROM `logs`
          WHERE `user_id` = l.`userid` AND `date_created` > l.`date_created`) < 3
GROUP BY `user_id`

Please note, I have not tested it so it may need a little tweaking.