下面的查询返回一组用户，对于每一行，从正在搜索的用户 (id = 4) 角度来看，有一些关系
SELECT `users`.`firstname` AS firstname,
`users`.`lastname` AS lastname,
COUNT(`trusted_users`.`id`) AS number_of_friend_in_common,
CASE ... AS friend,
CASE ... AS facebook_invitable,
CASE ... AS address_book_invitable,
CASE ... AS virtual_user,
FROM `users`
LEFT OUTER JOIN `trusted_users`
ON `trusted_users`.`user_id` = 4 AND `trusted_users`.`trust_user_id` = `users`.`id`
LEFT OUTER JOIN `facebook_friends`
ON (`facebook_friends`.`user_id` = 4 AND `facebook_friends`.`friend_user_id` = `users`.`id`
OR `facebook_friends`.`user_id` = `users`.`id` AND `facebook_friends`.`friend_user_id` = 4)
LEFT OUTER JOIN `address_book_contacts`
ON `address_book_contacts`.`owner_id` = 4 AND `address_book_contacts`.`email_digest` = `users`.`email_digest`
LEFT OUTER JOIN `friends`
ON (`friends`.`me_id` = `users`.`id` AND `friends`.`him_id` = 4
OR `friends`.`me_id` = 4 AND `friends`.`him_id` = `users`.`id`)
WHERE `users`.`id` NOT IN
(SELECT CASE
WHEN `friends`.`me_id` = 4 THEN `friends`.`him_id`
ELSE `friends`.`me_id`
END
FROM `friends`
WHERE (`friends`.`status` = 0
AND `friends`.`him_id` = 4
AND `friends`.`him_status` = 7
OR `friends`.`status` = 0
AND `friends`.`me_id` = 4
AND `friends`.`me_status` = 7))
AND (`users`.`firstname` LIKE '%a%' OR `users`.`lastname` LIKE '%a%')
GROUP BY `users`.`id`
ORDER BY friend DESC,
facebook_invitable DESC,
address_book_invitable DESC,
number_of_friend_in_common DESC,
virtual_user DESC,
firstname,
lastname LIMIT 0, 20
每个表的行数:
trusted_users:255k
facebook_friends:1k
address_book_contacts:1.5M
friend :70k
用户:32k
join的所有字段都有索引。查询需要 1.1 秒，这对于我们拥有的数据量来说是 Not Acceptable 。 我究竟做错了什么？我应该拆分多个查询并自己分页吗？
编辑 1: EXPLAIN 结果
+----+-------------+-----------------------+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------+---------+----------------------------------+-------+----------------------------------------------------------------------------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------------------+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------+---------+----------------------------------+-------+----------------------------------------------------------------------------------------------------------------------------+
| 1 | PRIMARY | users | ALL | PRIMARY,index_users_on_chat_id,index_users_login_facebook_id,index_users_on_login,index_users_on_parent_id,index_users_account_type,index_users_email_digest,index_users_id | NULL | NULL | NULL | 31847 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | trusted_users | ref | index_trusted_users_user,index_trusted_users_trust_user | index_trusted_users_trust_user | 5 | messenger_dev.users.id | 6 | Using where |
| 1 | PRIMARY | facebook_friends | index_merge | index_facebook_friends_user,index_facebook_friends_friend | index_facebook_friends_user,index_facebook_friends_friend | 5,5 | NULL | 2 | Using union(index_facebook_friends_user,index_facebook_friends_friend); Using where; Using join buffer (Block Nested Loop) |
| 1 | PRIMARY | address_book_contacts | ref | index_address_book_contacts_owner_id,index_address_book_contacts_email | index_address_book_contacts_email | 767 | messenger_dev.users.email_digest | 1 | Using where |
| 1 | PRIMARY | friends | index_merge | index_friends_me_him,index_friends_me,index_friends_him | index_friends_him,index_friends_me | 5,5 | NULL | 18 | Using union(index_friends_him,index_friends_me); Using where; Using join buffer (Block Nested Loop) |
| 2 | SUBQUERY | friends | index_merge | index_friends_me_him,index_friends_me,index_friends_him | index_friends_him,index_friends_me | 5,5 | NULL | 18 | Using union(index_friends_him,index_friends_me); Using where |
+----+-------------+-----------------------+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------+---------+----------------------------------+-------+----------------------------------------------------------------------------------------------------------------------------+
6 rows in set (0,00 sec)
编辑2:表结构
CREATE TABLE `address_book_contacts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`email_digest` varchar(191) DEFAULT NULL,
`code` varchar(191) DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
`owner_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `index_address_book_contacts_owner_id` (`owner_id`),
KEY `index_address_book_contacts_email` (`email_digest`)
) ENGINE=InnoDB AUTO_INCREMENT=1598109 DEFAULT CHARSET=utf8mb4;
CREATE TABLE `trusted_users` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`friend_id` int(11) DEFAULT NULL,
`user_id` int(11) DEFAULT NULL,
`trust_user_id` int(11) DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `index_trusted_users_on_friend_id` (`friend_id`),
KEY `index_trusted_users_user` (`user_id`),
KEY `index_trusted_users_trust_user` (`trust_user_id`),
CONSTRAINT `fk_rails_007c31c802` FOREIGN KEY (`trust_user_id`) REFERENCES `users` (`id`),
CONSTRAINT `fk_rails_ca24cb4e23` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=275576 DEFAULT CHARSET=utf8mb4;
CREATE TABLE `facebook_friends` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) DEFAULT NULL,
`friend_user_id` int(11) DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
`code` varchar(191) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `index_facebook_friends_user` (`user_id`),
KEY `index_facebook_friends_friend` (`friend_user_id`),
KEY `index_facebook_friends_code` (`code`(5)),
CONSTRAINT `fk_rails_78285a074e` FOREIGN KEY (`friend_user_id`) REFERENCES `users` (`id`),
CONSTRAINT `fk_rails_aa3ac53a81` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1149 DEFAULT CHARSET=utf8mb4;
CREATE TABLE `friends` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`me_id` int(11) DEFAULT NULL,
`him_id` int(11) DEFAULT NULL,
`owner_id` int(11) DEFAULT NULL,
`status` int(11) DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
`me_status` int(11) DEFAULT '0',
`him_status` int(11) DEFAULT '0',
PRIMARY KEY (`id`),
UNIQUE KEY `index_friends_me_him` (`me_id`,`him_id`),
KEY `index_friends_me` (`me_id`),
KEY `index_friends_him` (`him_id`),
KEY `index_friends_owner` (`owner_id`),
CONSTRAINT `fk_rails_9fa3474d31` FOREIGN KEY (`owner_id`) REFERENCES `users` (`id`),
CONSTRAINT `fk_rails_d3ebb6657f` FOREIGN KEY (`him_id`) REFERENCES `users` (`id`),
CONSTRAINT `fk_rails_fccfd1b821` FOREIGN KEY (`me_id`) REFERENCES `users` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=95724 DEFAULT CHARSET=utf8mb4;
CREATE TABLE `users` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`account_type` varchar(191) NOT NULL,
`firstname` varchar(191) DEFAULT NULL,
`lastname` varchar(191) DEFAULT NULL,
`login` varchar(191) DEFAULT NULL,
`avatar` varchar(191) DEFAULT NULL,
`gender` varchar(1) DEFAULT NULL,
`locale` varchar(191) DEFAULT NULL,
`birthdate` date DEFAULT NULL,
`password_digest` varchar(191) DEFAULT NULL,
`email_digest` varchar(191) DEFAULT NULL,
`created_at` datetime NOT NULL,
`updated_at` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `index_users_on_login` (`login`),
KEY `index_users_account_type` (`account_type`),
KEY `index_users_email_digest` (`email_digest`),
KEY `index_uses_firstname` (`firstname`),
KEY `index_users_lastname` (`lastname`)
) ENGINE=InnoDB AUTO_INCREMENT=32516 DEFAULT CHARSET=utf8mb4;
最佳答案
看起来 MySQL 没有为 users 表选择任何可用的索引。
首先，运行ANALYZE TABLE users;，然后重新运行EXPLAIN命令。第一个 rows 单元格的值现在是否大大低于 31847？如果是这样，您的问题就应该解决了!
如果没有，运行OPTIMIZE TABLE users;，然后重新运行EXPLAIN命令。第一个 rows 单元格的值现在是否大大低于 31847？如果是这样，您的问题就应该解决了!
如果这些步骤都没有帮助，请尝试在 FROM users 部分之后立即添加 USE INDEX (PRIMARY) 或 USE INDEX (users_id)您的查询。
希望这对您有所帮助!
关于mysql - 如何优化左连接上大数据的MySQL查询？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42093480/