SQL Multiple table JOINS, GROUP BY and HAVING - mysql

Question

I've a table structured somewhat similar to this:
CREATE TABLE `user`
(`id` int, `name` varchar(7));
CREATE TABLE `email`
(`id` int, `email_address` varchar(50), `verified_flag` tinyint(1),`user_id` int);
CREATE TABLE `social`
(`id` int,`user_id` int);
INSERT INTO `user`
(`id`, `name`)
VALUES
(1,'alex'),
(2,'jon'),
(3,'arya'),
(4,'sansa'),
(5,'hodor')
;
INSERT INTO `email`
(`id`,`email_address`,`verified_flag`,`user_id`)
VALUES
(1,'alex#gmail.com','1',1),
(2,'jon#gmail.com','0',1),
(3,'arya#gmail.com','0',3),
(4,'sansa#gmail.com','1',4),
(5,'reek#gmail.com','0',3),
(6,'hodor#gmail.com','0',5),
(7,'tyrion#gmail.com','0',1)
;
INSERT INTO `social`
(`id`,`user_id`)
VALUES
(1,4),
(2,4),
(3,5),
(4,4),
(5,4)
;
What I want to get is all emails:
which are not verified
which belongs to a user who has no, i.e 0, verified emails
which belongs to a user who has no, i.e 0, social records
With the below query I'm able to apply the 1st and 3rd condition but not the 2nd one:
SELECT *
FROM `email`
INNER JOIN `user` ON `user`.`id` = `email`.`user_id`
LEFT JOIN `social` ON `user`.`id` = `social`.`user_id`
WHERE `email`.`verified_flag` = 0
GROUP BY `email`.`user_id`,`email`.`email_address`
HAVING COUNT(`social`.`id`) = 0
How can I achieve the result?
Here's the sqlfiddle as well

Answer 1

Interesting and tricky one.
I see you've got something going on there. But having and sub queries becomes a VERY bad idea when your tables become large.
See below for an approach. Don't forget to set up your indexes!
SELECT * from email
LEFT JOIN social on email.user_id = social.user_id
-- tricky ... i'm going back to email table to pick verified emails PER user
LEFT JOIN email email2 on email2.user_id = email.user_id AND email2.verified_flag = 1
WHERE
-- you got this one going already :)
email.verified_flag = 0
-- user does not have any social record
AND social.id is null
-- email2 comes in handy here ... we limit resultset to include only users that DOES NOT have a verified email
AND email2.id is null
ORDER BY email.user_id asc;

Answer 2

You can use the following query:
SELECT e.`id`, e.`email_address`, e.`verified_flag`, e.`user_id`
FROM (
SELECT `id`,`email_address`,`verified_flag`,`user_id`
FROM `email`
WHERE `verified_flag` = 0) AS e
INNER JOIN (
SELECT `id`, `name`
FROM `user` AS t1
WHERE NOT EXISTS (SELECT 1
FROM `email` AS t2
WHERE `verified_flag` = 1 AND t1.`id` = t2.`user_id`)
AND
NOT EXISTS (SELECT 1
FROM `social` AS t3
WHERE t1.`id` = t3.`user_id`)
) AS u ON u.`id` = e.`user_id`;
This query uses two derived tables:
e implements the first condition, i.e. returns all emails which are not verified
u implements the 2nd and 3rd condition, i.e. it returns a set of all users that have no verified emails and have no social records.
Performing an INNER JOIN between e and u returns all emails satisfying condition no. 1 which belong to users satisfying conditions no. 2 and 3.
Demo here
You can alternatively use this query:
SELECT *
FROM `email`
WHERE `user_id` IN (
SELECT `email`.`user_id`
FROM `email`
INNER JOIN `user` ON `user`.`id` = `email`.`user_id`
LEFT JOIN `social` ON `user`.`id` = `social`.`user_id`
GROUP BY `email`.`user_id`
HAVING COUNT(`social`.`id`) = 0 AND
COUNT(CASE WHEN `email`.`verified_flag` = 1 THEN 1 END) = 0 )
The subquery is used in order to select all user_id satisfying conditions no. 2 and 3. Condition no. 1 is redundant since if the user has no verified emails, then there is no way a verified email is related to this user.
Demo here

Answer 3

Simply run a Union Query:
SELECT `user_id`, `email_address`, `verified_flag`, 'No Email' as `Type`
FROM `email` RIGHT JOIN `user` ON `user`.`id` = `email`.`user_id`
WHERE `email`.`user_id` IS NULL
UNION
SELECT `user_id`, `email_address`, `verified_flag`, 'Not Verified' as `Type`
FROM `email` INNER JOIN `user` ON `user`.`id` = `email`.`user_id`
WHERE `email`.`verified_flag` = 0
UNION
SELECT `user_id`, `email_address`, `verified_flag`, 'No Social' as `Type`
FROM `email` INNER JOIN `user` ON `user`.`id` = `email`.`user_id`
LEFT JOIN `social` ON `user`.`id` = `social`.`user_id`
GROUP BY `user_id`, `email_address`, `verified_flag`
HAVING COUNT(IFNULL(`social`.`id`, 0)) = 0;

Answer 4

SELECT
u.id AS u_id
, u.name AS u_name
, e.email_address AS e_email
, e.verified_flag AS e_verify
, e.user_id AS e_uid
, s.id AS s_id
, s.user_id AS u_id
, COALESCE(ver_e.ver_email_count,0) as ver_email_count
FROM
email as e
LEFT OUTER JOIN
user as u
ON u.id = e.user_id
LEFT OUTER JOIN
social AS s
ON u.id = s.user_id
LEFT OUTER JOIN
(
SELECT
COUNT(email_address) AS ver_email_count
, user_id
FROM
email
) AS ver_e
ON u.id = ver_e.user_id
GROUP BY
e.user_id
HAVING e.verified_flag = 0
AND
ver_email_count = 0
AND
ISNULL(s.id)
Uses one derived table to get the number of verified email addresses each user has got