MySQL - GROUP BY slow down the page - php

Question

GROUP BY clause in the query below slow down the page, please help to resolve this issue
SELECT
`a`.*,
CONCAT(a.`firstname`, " ", a.`lastname`) AS `cont_name`,
CONCAT(a.`position`, " / ", a.`company`) AS `comp_pos`,
CONCAT(f.`firstname`, " ", f.`lastname`) AS `created_by`
FROM
`contacts` AS `a`
LEFT JOIN `users` AS `f` ON f.id = a.user_id
LEFT JOIN `user_centres` AS `b` ON a.user_id = b.user_id
WHERE b.centre_id IN (23, 24, 25, 26, 20, 21, 22, 27, 28)
GROUP BY `a`.`id`
ORDER BY `a`.`created` desc
Here the join with user_centres table is for centre wise filtering of data. EXPLAIN gives the result as:
- 1 SIMPLE a index PRIMARY,user_id,area_id,industry_id,country PRIMARY 4 NULL 20145 Using temporary; Using filesort
Our requirement is as below
Listing of all contacts in admin login
Centre wise listing of contacts in manager/clerk login
Total records in contact table is > 20K.
There will be multiple entry for users in user_centres table, ie: a user is assigned to more than one centre.
While executing the query in server by excluding GROUP BY is nearly 300k data which makes the problem.
Db stucture
Table structure for table contacts
CREATE TABLE IF NOT EXISTS `contacts` (
`id` int(11) NOT NULL,
`user_id` int(11) DEFAULT NULL,
`imported` tinyint(4) NOT NULL DEFAULT '0',
`situation` char(10) DEFAULT NULL,
`firstname` varchar(150) DEFAULT NULL,
`lastname` varchar(150) DEFAULT NULL,
`position` varchar(150) DEFAULT NULL,
`dob` datetime DEFAULT NULL,
`office_contact` varchar(100) DEFAULT NULL,
`mobile_contact` varchar(100) DEFAULT NULL,
`email` varchar(255) NOT NULL,
`company` varchar(150) DEFAULT NULL,
`industry_id` int(11) DEFAULT NULL,
`address` varchar(255) DEFAULT NULL,
`city` varchar(150) DEFAULT NULL,
`country` int(11) DEFAULT NULL,
`isclient` tinyint(4) NOT NULL DEFAULT '0',
`classification` varchar(100) DEFAULT NULL,
`created` datetime NOT NULL,
`updated` datetime NOT NULL,
`unsubscribe` enum('Y','N') NOT NULL DEFAULT 'N'
) ENGINE=InnoDB AUTO_INCREMENT=25203 DEFAULT CHARSET=latin1;
Indexes for table contacts
ALTER TABLE `contacts`
ADD PRIMARY KEY (`id`), ADD KEY `user_id` (`user_id`),
ADD KEY `industry_id` (`industry_id`), ADD KEY `country` (`country`);
Constraints for table contacts
ALTER TABLE `contacts`
ADD CONSTRAINT `contacts_ibfk_4` FOREIGN KEY (`user_id`)
REFERENCES `users` (`id`) ON DELETE SET NULL ON UPDATE NO ACTION,
ADD CONSTRAINT `contacts_ibfk_6` FOREIGN KEY (`industry_id`)
REFERENCES `industries` (`id`) ON DELETE SET NULL ON UPDATE NO ACTION,
ADD CONSTRAINT `contacts_ibfk_7` FOREIGN KEY (`country`)
REFERENCES `country` (`id`) ON DELETE SET NULL ON UPDATE NO ACTION;
Table structure for table users
CREATE TABLE IF NOT EXISTS `users` (
`id` int(11) NOT NULL,
`role_id` int(11) NOT NULL,
`email` varchar(250) NOT NULL,
`password` varchar(45) NOT NULL,
`salt` varchar(45) DEFAULT NULL,
`status_id` int(11) DEFAULT NULL,
`status` tinyint(1) DEFAULT '1',
`firstname` varchar(255) NOT NULL,
`lastname` varchar(255) NOT NULL,
`created` datetime DEFAULT NULL,
`updated` datetime DEFAULT NULL
) ENGINE=InnoDB AUTO_INCREMENT=30 DEFAULT CHARSET=latin1;
Indexes for table users
ALTER TABLE `users`
ADD PRIMARY KEY (`id`), ADD UNIQUE KEY `email_UNIQUE` (`email`),
ADD KEY `type_id_idx` (`role_id`), ADD KEY `status_id_idx` (`status_id`);
Constraints for table users
ALTER TABLE `users`
ADD CONSTRAINT `role_id` FOREIGN KEY (`role_id`)
REFERENCES `users_roles` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
ADD CONSTRAINT `status_id` FOREIGN KEY (`status_id`)
REFERENCES `users_status` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
ADD CONSTRAINT `users_ibfk_1` FOREIGN KEY (`area`)
REFERENCES `area` (`id`) ON DELETE SET NULL ON UPDATE NO ACTION;
Table structure for table user_centres
CREATE TABLE IF NOT EXISTS `user_centres` (
`id` int(11) NOT NULL,
`user_id` int(11) NOT NULL,
`area_id` int(11) NOT NULL,
`centre_id` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=72 DEFAULT CHARSET=utf8;
Indexes for table user_centres
ALTER TABLE `user_centres`
ADD PRIMARY KEY (`id`), ADD KEY `user_id` (`user_id`),
ADD KEY `centre_id` (`centre_id`), ADD KEY `area_id` (`area_id`);
Constraints for table user_centres
ALTER TABLE `user_centres`
ADD CONSTRAINT `user_centres_ibfk_1` FOREIGN KEY (`user_id`)
REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION,
ADD CONSTRAINT `user_centres_ibfk_2` FOREIGN KEY (`centre_id`)
REFERENCES `centre` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION;
Also please refer EXPLAIN screens - http://prntscr.com/6o5h8s

Answer 1

Index were not used because of the different ORDER BY a GROUP BY clauses.
http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html

Answer 2

You are spending a lot of time checking user_centres, but not needing anything from it. Remove it from the query.
users can be made into a correlates subquery:
SELECT `a`.*,
CONCAT(a.`firstname`, " ", a.`lastname`) AS `cont_name`,
CONCAT(a.`position`, " / ", a.`company`) AS `comp_pos`,
( SELECT CONCAT(f.`firstname`, " ", f.`lastname`)
FROM `users` AS `f` ON f.id = a.user_id
) AS `created_by`
FROM `contacts` AS `a`
GROUP BY `a`.`id`
ORDER BY `a`.`created` desc
Do you really need all 20K rows?? The sheer bulk of the result is part of the sluggishness.

Answer 3

Thanks all, based on the feedback got from all of you I have tried the query below now and give me the speed improvement from 30 secs to 15 secs
SELECT `a`.`id`, `a`.`user_id`, `a`.`imported`, `a`.`created`,
`a`.`unsubscribe`, CONCAT(a.firstname, " ", a.lastname) AS `cont_name`,
CONCAT(a.position, " / ", a.company) AS `comp_pos`,
( SELECT COUNT(uc.id)
FROM `user_centres` AS `uc`
WHERE (uc.user_id = a.user_id)
AND (uc.centre_id IN (29))
GROUP BY `uc`.`user_id`
) AS `centre_cnt`,
( SELECT GROUP_CONCAT(DISTINCT g.group_name
ORDER BY g.group_name ASC SEPARATOR ", ")
FROM `groups` AS `g`
INNER JOIN `group_contacts` AS `gc` ON g.id = gc.group_id
WHERE (gc.contact_id = a.id)
GROUP BY `gc`.`contact_id`
) AS `group_name`,
( SELECT CONCAT(u.`firstname`, " ", u.`lastname`)
FROM `users` AS `u`
WHERE (u.id = a.user_id)
) AS `created_by`, `e`.`name` AS `industry_name`
FROM `contacts` AS `a`
LEFT JOIN `industries` AS `e` ON e.id = a.industry_id
WHERE (1)
HAVING (centre_cnt is NOT NULL)
ORDER BY `a`.`id` desc
Let me know Is there a way to improve the speed and make the page loading below 5 secs.
Please see the interface (noted the filtering and sorting fields) - http://prntscr.com/6q6q70