Question

We have a central login that we use to support multiple websites. To store our users’ data we have an accounts table which stores each user account and then users tables for each site for site specific information. We also have a simple connections table which stores the connections between users.

We noticed that one query that is joining the tables on their primary key user_id is executing slowly. I’m hoping that some SQL expert out there can explain why it’s using WHERE to search the users_site1 table and suggest how we can optimize it. Here is the slow query & the explain results:

mysql> explain select a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews from accounts a join users_site1 u ON a.user_id=u.user_id where a.user_id IN (select cid2 from connections where cid1=10001006 AND type="MM" AND status="A") OR a.user_id IN (select cid1 from connections where cid2=10001006 AND type="MM" AND status="A") order by RAND() LIMIT 4;
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
| id | select_type        | table       | type   | possible_keys     | key     | key_len | ref                   | rows  | Extra                                        |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
|  1 | PRIMARY            | u           | ALL    | PRIMARY           | NULL    | NULL    | NULL                  | 79783 | Using where; Using temporary; Using filesort |
|  1 | PRIMARY            | a           | eq_ref | PRIMARY           | PRIMARY | 4       | exampledb.u.user_id |     1 |                                              |
|  3 | DEPENDENT SUBQUERY | connections | ref    | PRIMARY,cid1,cid2 | cid2    | 6       | const,const           |     2 | Using where                                  |
|  2 | DEPENDENT SUBQUERY | connections | ref    | PRIMARY,cid1,cid2 | cid1    | 6       | const,const           |     1 | Using where                                  |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
4 rows in set (0.00 sec)

Here are the definitions for each table:

CREATE TABLE `accounts` (
  `user_id` int(9) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(40) DEFAULT NULL,
  `facebook_id` bigint(15) unsigned DEFAULT NULL,
  `facebook_username` varchar(30) DEFAULT NULL,
  `password` varchar(20) DEFAULT NULL,
  `profile_photo` varchar(100) DEFAULT NULL,
  `first_name` varchar(40) DEFAULT NULL,
  `middle_name` varchar(40) DEFAULT NULL,
  `last_name` varchar(40) DEFAULT NULL,
  `suffix_name` char(3) DEFAULT NULL,
  `organization_name` varchar(100) DEFAULT NULL,
  `organization` tinyint(1) unsigned DEFAULT NULL,
  `address` varchar(200) DEFAULT NULL,
  `city` varchar(40) DEFAULT NULL,
  `state` varchar(20) DEFAULT NULL,
  `zip` varchar(10) DEFAULT NULL,
  `province` varchar(40) DEFAULT NULL,
  `country` int(3) DEFAULT NULL,
  `latitude` decimal(11,7) DEFAULT NULL,
  `longitude` decimal(12,7) DEFAULT NULL,
  `phone` varchar(20) DEFAULT NULL,
  `sex` char(1) DEFAULT NULL,
  `birthday` date DEFAULT NULL,
  `about_me` varchar(2000) DEFAULT NULL,
  `activities` varchar(300) DEFAULT NULL,
  `website` varchar(100) DEFAULT NULL,
  `email` varchar(150) DEFAULT NULL,
  `referrer` int(4) unsigned DEFAULT NULL,
  `referredid` int(9) unsigned DEFAULT NULL,
  `verify` int(6) DEFAULT NULL,
  `status` char(1) DEFAULT 'R',
  `created` datetime DEFAULT NULL,
  `verified` datetime DEFAULT NULL,
  `activated` datetime DEFAULT NULL,
  `network` datetime DEFAULT NULL,
  `deleted` datetime DEFAULT NULL,
  `logins` int(6) unsigned DEFAULT '0',
  `api_logins` int(6) unsigned DEFAULT '0',
  `last_login` datetime DEFAULT NULL,
  `last_update` datetime DEFAULT NULL,
  `private` tinyint(1) unsigned DEFAULT NULL,
  `ip` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`user_id`),
  UNIQUE KEY `username` (`username`),
  KEY `facebook_id` (`facebook_id`),
  KEY `status` (`status`),
  KEY `state` (`state`)
);

CREATE TABLE `users_site1` (
  `user_id` int(9) unsigned NOT NULL,
  `facebook_id` bigint(15) unsigned DEFAULT NULL,
  `facebook_username` varchar(30) DEFAULT NULL,
  `facebook_publish` tinyint(1) unsigned DEFAULT NULL,
  `facebook_checkin` tinyint(1) unsigned DEFAULT NULL,
  `facebook_offline` varchar(300) DEFAULT NULL,
  `twitter_id` varchar(60) DEFAULT NULL,
  `twitter_secret` varchar(50) DEFAULT NULL,
  `twitter_username` varchar(20) DEFAULT NULL,
  `type` char(1) DEFAULT 'M',
  `referrer` int(4) unsigned DEFAULT NULL,
  `referredid` int(9) unsigned DEFAULT NULL,
  `session` varchar(60) DEFAULT NULL,
  `api_session` varchar(60) DEFAULT NULL,
  `status` char(1) DEFAULT 'R',
  `created` datetime DEFAULT NULL,
  `verified` datetime DEFAULT NULL,
  `activated` datetime DEFAULT NULL,
  `deleted` datetime DEFAULT NULL,
  `logins` int(6) unsigned DEFAULT '0',
  `api_logins` int(6) unsigned DEFAULT '0',
  `last_login` datetime DEFAULT NULL,
  `last_update` datetime DEFAULT NULL,
  `ip` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`user_id`)
);

CREATE TABLE `connections` (
  `cid1` int(9) unsigned NOT NULL DEFAULT '0',
  `cid2` int(9) unsigned NOT NULL DEFAULT '0',
  `cid3` int(9) unsigned NOT NULL DEFAULT '0',
  `type` char(2) NOT NULL,
  `status` char(1) NOT NULL,
  `created` datetime DEFAULT NULL,
  `updated` datetime DEFAULT NULL,
  PRIMARY KEY (`cid1`,`cid2`,`type`,`cid3`),
  KEY `cid1` (`cid1`,`type`),
  KEY `cid2` (`cid2`,`type`)
);

Answer 1

Instead of WHERE a.userid IN( ... ) OR a.userid IN( ... ) you should use another join:

select 
a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,
a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews 
from accounts a 
join users_site1 u ON a.user_id=u.user_id 
join ( select cid2 as id from connections 
       where cid1=10001006 AND type="MM" AND status="A"
       union
       select cid1 as id from connections
       where cid2=10001006 AND type="MM" AND status="A" ) c
on a.user_id = c.id
order by RAND() LIMIT 4;