Question

This is by far the slowest query in my web application.

SELECT prof.user_id                      AS userId,
       prof.first_name                   AS first,
       prof.last_name                    AS last,
       prof.birthdate,
       prof.class_string                 AS classes,
       prof.city,
       prof.country,
       prof.state,
       prof.images,
       prof.videos,
       u.username,
       u.avatar,
       (SELECT Count(*)
        FROM   company_member_sponsorship
        WHERE  member_id = prof.user_id
               AND status = 'sponsored') AS sponsor_count,
       (SELECT Count(*)
        FROM   member_schedules
        WHERE  user_id = prof.user_id)   AS sched_count
FROM   member_profiles prof
       LEFT JOIN users u
              ON u.id = prof.user_id
ORDER  BY ( prof.images + prof.videos * 5 + (
            CASE
              WHEN prof.expire_date > :time THEN 50
              ELSE 0
            end ) + sponsor_count * 20 + sched_count * 4
          ) DESC,
          prof.last_name ASC
LIMIT  :start, :records  

Everything else on the site takes less than a second to load even with lots of queries happening on all levels. This one takes about 3-4 seconds.

It’s obviously the table scans that are causing the slowdown. I can understand why; the first table has 50,000+ rows, the second 160,000+ rows.

Is there any way I can optimize this query to make it go faster?

If worse comes to worst I can always go through my code and maintain a tally for sponsorships and events in the profile table like I do for images and videos though I’d like to avoid it.

EDIT: I added the results of an EXPLAIN on the query.

id  select_type         table                       type    possible_keys   key         key_len ref                         rows    Extra
1   PRIMARY             prof                        ALL     NULL            NULL        NULL    NULL                        44377   Using temporary; Using filesort
1   PRIMARY             u                           eq_ref  PRIMARY         PRIMARY     3       mxsponsor.prof.user_id      1   
3   DEPENDENT SUBQUERY  member_schedules            ref     user_id         user_id     3       mxsponsor.prof.user_id      6       Using index
2   DEPENDENT SUBQUERY  company_member_sponsorship  ref     member_id       member_id   3       mxsponsor.prof.user_id      2       Using where; Using index

EDIT2:

I ended up dealing with the problem by maintaining a count in the member profile. Wherever sponsorships/events are added/deleted I just invoke a function that scans the sponsorship/events table and updates the count for that member. There might still be a way to optimize a query like this, but we’re publishing this site rather soon so I’m going with the quick and dirty solution for now.

Answer 1

Not guaranteed to work, but try using join and group by rather than inner selects:

SELECT prof.user_id      AS userId,
       prof.first_name   AS first,
       prof.last_name    AS last,
       prof.birthdate,
       prof.class_string AS classes,
       prof.city,
       prof.country,
       prof.state,
       prof.images,
       prof.videos,
       u.username,
       u.avatar,
       Count(cms.id)     AS sponsor_count,
       Count(ms.id)      AS sched_count
FROM   member_profiles prof
       LEFT JOIN users u
              ON u.id = prof.user_id
       LEFT JOIN company_member_sponsorship cms
              ON cms.member_id = prof.user_id
                 AND cms.status = 'sponsored'
       LEFT JOIN member_schedules ms
              ON ms.user_id = prof.user_id
GROUP  BY u.id
ORDER  BY ( prof.images + prof.videos * 5 + (
            CASE
              WHEN prof.expire_date > :time THEN 50
              ELSE 0
            end ) + sponsor_count * 20 + sched_count * 4
          ) DESC,
          prof.last_name ASC
LIMIT  :start, :records  

If that’s not any better, a explain of that query would help.