Question

This query is running very slow; it used to be 3 separate queries but I’ve consolidated it into 1. I assume it’s slow because of the subselects it’s doing, but I assume there might be a better way to query for this info.

* Background:*

users is just user accounts.
posts is all the post content.
posts_int is just 2 fields, postid and intid. This stores interest ID’s for posts.
int_usr is also just 2 fields, userid and intid. This stores interest ID’s for users.

All of the “intid” field names are based on another table that simply has ids and names for each interest. This query returns all posts for this user that are relevant to their selected interests, stored in integers in int_usr.

The query:

SELECT DISTINCT 
users.first_name,
users.last_name,
posts.id,
posts.userid,
posts.comments,
posts.date,
posts.comment 
FROM posts 
LEFT JOIN users ON 
posts.userid = users.id 
LEFT JOIN posts_int ON 
posts.id = posts_int.postid 
WHERE 
posts_int.intid IN (
SELECT DISTINCT 
  intid 
FROM int_usr 
WHERE 
  intid IN (
      SELECT DISTINCT 
      intid 
       FROM int_usr 
       WHERE 
      userid = '1' 
  ) 
ORDER BY intid ASC 
)
AND posts.deleted = '0' 
AND users.deleted = '0' 
ORDER BY 
posts.id DESC 
LIMIT 0,12

Any help is appreciated!

Ryan

EDIT: Here is the explain you requested:

* EXPLAIN SQL: *

+----+--------------------+-----------+--------+----------------+---------+---------+---------------------------+------+----------------------------------------------+
| id | select_type        | table     | type   | possible_keys  | key     | key_len | ref                       | rows | Extra                                        |
+----+--------------------+-----------+--------+----------------+---------+---------+---------------------------+------+----------------------------------------------+
|  1 | PRIMARY            | posts_int | ALL    | postid         | NULL    | NULL    | NULL                      |   87 | Using where; Using temporary; Using filesort |
|  1 | PRIMARY            | posts     | eq_ref | PRIMARY,userid | PRIMARY | 4       | bunchify.posts_int.postid |    1 | Using where                                  |
|  1 | PRIMARY            | users     | eq_ref | PRIMARY        | PRIMARY | 4       | bunchify.posts.userid     |    1 | Using where                                  |
|  2 | DEPENDENT SUBQUERY | int_usr   | ALL    | NULL           | NULL    | NULL    | NULL                      |  288 | Using where; Using temporary                 |
|  3 | DEPENDENT SUBQUERY | int_usr   | ref    | userid         | userid  | 4       | const                     |   19 | Using where; Using temporary                 |
+----+--------------------+-----------+--------+----------------+---------+---------+---------------------------+------+----------------------------------------------+
5 rows in set (0.00 sec)

Answer 1

You can simplify things a bit by getting rid of the extra level of nesting in

posts_int.intid IN (
SELECT DISTINCT 
  intid 
FROM int_usr 
WHERE 
  intid IN (
      SELECT DISTINCT 
      intid 
       FROM int_usr 
       WHERE 
      userid = '1' 
  ) 
ORDER BY intid ASC 
)

and then changing the left joins to inner joins because you’re checking the right tables in your where clause anyways.

---

Something like

SELECT DISTINCT <blah>
  FROM posts 
  JOIN users 
       ON posts.userid = users.id 
  JOIN posts_int 
       ON posts.id = posts_int.postid 
  JOIN int_usr 
       on posts_int.intid = int_usr.intid and int_usr.userid = '1'
 where posts.deleted = '0' 
   AND users.deleted = '0' 
ORDER BY posts.id DESC 
LIMIT 0,12