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 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.user_id as 'id',a.username,a.first_name as 'first',a.last_name as 'last',a.sex,u.user_id as 'profile',u.facebook_id as 'fb_id',u.facebook_publish as 'fb_publish',u.facebook_offline as 'fb_offline',u.twitter_id as 'tw_id',u.api_session as 'mobile',a.network from accounts a left join users_site1 u ON a.user_id=u.user_id AND u.status="R" where a.status="R" AND u.status="R" AND a.facebook_id='1234567890';
+----+-------------+-------+--------+----------------+---------+---------+-----------------------+-------+-------------+
| id | select_type | table | type   | possible_keys  | key     | key_len | ref                   | rows  | Extra       |
+----+-------------+-------+--------+----------------+---------+---------+-----------------------+-------+-------------+
|  1 | SIMPLE      | u     | ALL    | PRIMARY        | NULL    | NULL    | NULL                  | 79769 | Using where |
|  1 | SIMPLE      | a     | eq_ref | PRIMARY,status | PRIMARY | 4       | alltrailsdb.u.user_id |     1 | Using where |
+----+-------------+-------+--------+----------------+---------+---------+-----------------------+-------+-------------+
2 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 `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`)
);

Answer 1

Add a index on the column facebook_id in the accounts table.

Current, MySql is scanning the entire users table, since it cannot find the record directly in the account table.