Home/ Questions/Q 9227837
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-18T05:10:42+00:00

I’m looking to speed up this query somehow. Possibly to the point where its

  • 0

I’m looking to speed up this query somehow. Possibly to the point where its acceptable to run it on a low traffic site. It takes 15+ seconds which is way too long.

Currently there are 13k rows in the table, which is approx 1 months data, however i’m expecting that monthly data to double once the site is in production. The aim is to select the top 10 gains for the last week.

there are two tables, users table and the tracker table, in the tracker table there are multiple rows for each user, at least 8 per day, per user.

The aim of the query is to take the latest row for each user, subtract from that a value from a row inserted 1 week ago to get the amount of xp they have gained and select the top 10 highest gainers.

Table schema (which im sure could be improved too)

users table

id int(11) primary
rsn varchar(12) unique
joined timestamp
disabled bool

tracker table

id int(11) primary
user_id int(11) index /* Associated with the id in the users table */
timestamp timestamp
overall_rank int(11)
overall_level int(4)
overall_exp int(10)

And the query.

SELECT  `users`.`rsn` ,  `tracker`.`timestamp` , @uid :=  `tracker`.`user_id` , (
    SELECT  `overall_exp` 
    FROM  `tracker` 
    WHERE  `user_id` = @uid 
    ORDER BY  `timestamp` DESC 
    LIMIT 1
) - (
    SELECT  `overall_exp` 
    FROM  `tracker` 
    WHERE  `timestamp` >= SUBDATE( NOW( ) , INTERVAL 1 WEEK ) 
    AND  `user_id` = @uid 
    ORDER BY  `timestamp` ASC 
    LIMIT 1 ) AS  `gained_exp` 
FROM  `tracker` 
JOIN  `users` ON  `tracker`.`user_id` =  `users`.`id` 
ORDER BY  `gained_exp` DESC 
LIMIT 10

Explain output

+----+----------------------+---------+-------+---------------+---------+---------+------------------+-------+----------------------------------------------+
| id | select_type          | table   | type  | possible_keys | key     | key_len | ref              | rows  | Extra                                        |
+----+----------------------+---------+-------+---------------+---------+---------+------------------+-------+----------------------------------------------+
|  1 | PRIMARY              | users   | index | PRIMARY       | rsn     | 14      | NULL             |    71 | Using index; Using temporary; Using filesort |
|  1 | PRIMARY              | tracker | ref   | user_id       | user_id | 4       | surreal.users.id |   103 |                                              |
|  3 | UNCACHEABLE SUBQUERY | tracker | ALL   | NULL          | NULL    | NULL    | NULL             | 11752 | Using where; Using filesort                  |
|  2 | UNCACHEABLE SUBQUERY | tracker | ALL   | NULL          | NULL    | NULL    | NULL             | 11752 | Using where; Using filesort                  |
+----+----------------------+---------+-------+---------------+---------+---------+------------------+-------+----------------------------------------------+
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Try avoiding the correlated subqueries by first finding the timestamps for today and 1 week ago for all users, then joining twice again to tracker to find the corresponding values of overall_exp before doing the calculation:

    SELECT rsn, ts.thisweek, ts.user_id,
       last.overall_exp - previous.overall_exp AS gained_exp
FROM (SELECT user_id, MIN(timestamp) AS lastweek, MAX(timestamp) AS thisweek
      FROM tracker
      WHERE timestamp >= SUBDATE(NOW(), INTERVAL 1 WEEK)
      GROUP BY user_id) AS ts
INNER JOIN tracker previous
ON previous.user_id = ts.user_id AND previous.timestamp = ts.lastweek
INNER JOIN tracker last
ON last.user_id = ts.user_id AND last.timestamp = ts.thisweek
JOIN users ON ts.user_id = users.id
ORDER BY gained_exp DESC
LIMIT 10
    • 0