MySql query is slow with join - how to speed it up - mysql

Question

I have to export 554k records from our mysql db. At the current rate it will take 5 days to export the data and the slowness is mainly caused by the query below. The data structure consists of
Companies
--Contacts
----(Contact)Activities
For the contacts, we have an index on company_id. On the activities table, we have an index for contact_id and company_id which map back to the respective contacts and companies tables.
I need to grab each contact and the latest activity date that they have. This is the query that I'm running and it takes about .5 second to execute.
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
If I remove the join and just select * from contacts where company_id=20 the query executes in .016 sec.
If I use Explain for info on the join query I get this
Any ideas on how I can speed this up?
Edit:
Here are the table definitions.
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;

Answer 1

This is a greatest-n-per-group query, which comes up frequently on Stack Overflow.
Here's a solution that uses a MySQL 8.0 window function:
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
Here's a solution that should work on pre-8.0 versions:
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;
Another solution:
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
It would be helpful to create a new index on activities (contact_id, occurred_at).

Answer 2

Don't use subqueries in the FROM clause if you can help it. They impede the MySQL optimizer. So, if you want one row:
Select c.*, a.occurred_at
from contacts c left outer join
from activities a
on c.id = a.contact_id and
a.occurred_at is not null
where c.company_id = 20
order by a.occurred_at desc
limit 1;
If you want one row per contact_id:
Select c.*, a.occurred_at
from contacts c left outer join
from activities a
on c.id = a.contact_id and
a.occurred_at is not null and
a.occurred_at = (select max(a2.occurred_at)
from activities a2
where a2.contact_id = a.contact_id
)
where c.company_id = 20
order by a.occurred_at desc
limit 1;
This can make use of an index on activities(contact_id, occured_at). and contact(company_id, contact_id).
Your query is doing one thing that is a clear no-no -- and no longer supported by the default settings in the most recent versions of MySQL. You have unaggregated columns in a select that are not in the group by. The contact_id should be generating an error.

Answer 3

I feel like I am overlooking something with how complicated the other answers are, but I would think this would be all you need.
SELECT c.*
, MAX(a.occurred_at) AS occurred_at
FROM contacts AS c
LEFT JOIN activities AS a
ON c.id = a.contact_id AND a.occurred_at IS NOT NULL
WHERE c.company_id = 20
GROUP BY c.id;
Notes: (1) this assumes you didn't actually want the duplicate contact_id from your original subquery to be in the final results. (2) This also assumes your server is not configured to require a full group by; if it is, you will need to manually expand c.* into the full column list, and copy that list to the GROUP BY clause as well.
Expanding on dnoeth's comments to your question; if you are not querying each company separately for a particular reason (chunking for load, code structure handling this also handles other stuff company by company, whatever), you could tweak the above query like so to get all your results in one query.
SELECT con.*
, MAX(a.occurred_at) AS occurred_at
FROM companies AS com
INNER JOIN contacts AS con ON com.id = con.company_id
LEFT JOIN activities AS a
ON con.id = a.contact_id AND a.occurred_at IS NOT NULL
WHERE [criteria for companies chosen to be queried]
GROUP BY con.id
ORDER BY con.company_id, con.id
;