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MySQL查询连接慢-如何加快速度

2019-11-08 09:14:44 作者：互联网

我必须从我们的mysql数据库中导出554k记录.以目前的速度,导出数据将需要5天,并且速度缓慢主要是由以下查询引起的.数据结构包括

Companies
--Contacts
----(Contact)Activities

对于联系人,我们在company_id上有一个索引.在活动表上,我们有一个contact_id和company_id的索引,它们分别映射回相应的contact和company表.

我需要获取每个联系人及其最新的活动日期.这是我正在运行的查询,执行大约需要0.5秒.

Select * 
from contacts 
left outer join (select  occurred_at
                        ,contact_id 
                 from activities 
                 where occurred_at is not null 
                 group by contact_id 
                 order by occurred_at desc) activities 
on contacts.id = activities.contact_id 
where company_id = 20

如果我删除联接并仅从company_id = 20的联系人中选择*,则查询将在.016秒内执行.

如果我使用Explain获取有关联接查询的信息,则会得到此信息

关于如何加快速度的任何想法？

编辑：
这是表定义.

CREATE TABLE `companies` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `street_address` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `city` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `state` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `county` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `website` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `external_id` int(11) DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  `user_id` int(11) DEFAULT NULL,
  `falloff_date` date DEFAULT NULL,
  `zipcode` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `phone` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `company_id` int(11) DEFAULT NULL,
  `order_count` int(11) NOT NULL DEFAULT '0',
  `active_job_count` int(11) NOT NULL DEFAULT '0',
  `duplicate_of` int(11) DEFAULT NULL,
  `warm_date` datetime DEFAULT NULL,
  `employee_size` int(11) DEFAULT NULL,
  `dup_checked` tinyint(1) DEFAULT '0',
  `rating` int(11) DEFAULT NULL,
  `delinquent` tinyint(1) DEFAULT '0',
  `cconly` tinyint(1) DEFAULT '0',
  PRIMARY KEY (`id`),
  KEY `index_companies_on_name` (`name`),
  KEY `index_companies_on_user_id` (`user_id`),
  KEY `index_companies_on_company_id` (`company_id`),
  KEY `index_companies_on_external_id` (`external_id`),
  KEY `index_companies_on_state_and_dup_checked` (`id`,`state`,`dup_checked`,`duplicate_of`),
  KEY `index_companies_on_dup_checked` (`id`,`dup_checked`),
  KEY `index_companies_on_dup_checked_name` (`dup_checked`,`name`),
  KEY `index_companies_on_county` (`county`,`state`)
) ENGINE=InnoDB AUTO_INCREMENT=15190300 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


CREATE TABLE `contacts` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `first_name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `last_name` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `title` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `phone` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `extension` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `fax` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `email` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `active` tinyint(1) DEFAULT NULL,
  `main` tinyint(1) DEFAULT NULL,
  `company_id` int(11) DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  `external_id` int(11) DEFAULT NULL,
  `second_phone` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `index_contacts_on_company_id` (`company_id`),
  KEY `index_contacts_on_first_name` (`first_name`),
  KEY `index_contacts_on_last_name` (`last_name`),
  KEY `index_contacts_on_phone` (`phone`),
  KEY `index_contacts_on_email` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=11241088 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


CREATE TABLE `activities` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `kind` int(11) DEFAULT NULL,
  `contact_id` int(11) DEFAULT NULL,
  `call_status` int(11) DEFAULT NULL,
  `occurred_at` datetime DEFAULT NULL,
  `notes` text COLLATE utf8_unicode_ci,
  `user_id` int(11) DEFAULT NULL,
  `scheduled_for` datetime DEFAULT NULL,
  `priority` tinyint(1) DEFAULT NULL,
  `company_id` int(11) DEFAULT NULL,
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  `from_user_id` int(11) DEFAULT NULL,
  `to_user_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `index_activities_on_contact_id` (`contact_id`),
  KEY `index_activities_on_user_id` (`user_id`),
  KEY `index_activities_on_company_id` (`company_id`)
) ENGINE=InnoDB AUTO_INCREMENT=515340 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

解决方法:

这是一个greatest-n-per-group查询,经常在堆栈溢出中出现.

这是使用MySQL 8.0窗口函数的解决方案：

WITH latest_activities AS (
  SELECT contact_id, occurred_at,
    ROW_NUMBER() OVER (PARTITION BY contact_id ORDER BY occurred_at DESC) AS rn
  FROM activities
)
SELECT *
FROM contacts AS c
LEFT OUTER JOIN latest_activities 
  ON c.id = latest_activities.contact_id AND latest_activities.rn = 1
WHERE c.company_id = 20

以下是适用于8.0之前版本的解决方案：

SELECT c.*, a.*
FROM contacts AS c
LEFT OUTER JOIN activities AS a ON a.contact_id = c.id
LEFT OUTER JOIN activities AS a2 ON a2.contact_id = c.id 
  AND a2.occurred_at > a.occurred_at
WHERE c.company_id = 20
  AND a2.contact_id IS NULL;

另一个解决方案：

SELECT c.*, a.*
FROM contacts AS c
LEFT OUTER JOIN activities AS a ON a.contact_id = c.id
LEFT OUTER JOIN (
  SELECT c2.contact_id, MAX(a2.occurred_at) AS occurred_at
  FROM activities AS a2
  INNER JOIN contacts AS c2 ON a2.contact_id = c2.id
  WHERE c2.company_id = 20 
  GROUP BY c2.contact_id ORDER BY NULL
) AS latest_activities
  ON latest_activities.contact_id = c.id
  AND latest_activities.occurred_at = a.occurred_at
WHERE c.company_id = 20

创建有关活动的新索引(contact_id,发生_at)将很有帮助.

标签：sql,mysql,greatest-n-per-group
来源： https://codeday.me/bug/20191108/2006779.html