sql query to get friends based on email - mysql

Question

I have sample data that looks like this
| users |
| user_id | email |
|---------|--------------------------|
| 1 | test#example.com |
| 2 | Kanchhi#example.com |
| 3 | modi#example.com |
| 4 | andy#example.com |
| 5 | maya#example.com |
| 6 | jetli#example.com |
| 7 | john#example.com |
| user_relations |
| user_relation_id | requestor_user_id | receiver_user_id | friend_status |
|------------------|-------------------|------------------|---------------|
| 1 | 2 | 4 | 1 |
| 2 | 2 | 6 | 1 |
| 3 | 2 | 7 | 1 |
| 4 | 5 | 2 | NULL |
| 5 | 5 | 7 | NULL |
| 6 | 7 | 2 | NULL |
| 7 | 7 | 4 | 1 |
| 8 | 7 | 5 | 1 |
| 9 | 7 | 6 | 1 |
| 10 | 4 | 2 | 1 |
| 11 | 4 | 3 | 1 |
| 12 | 4 | 5 | 1 |
| 13 | 4 | 6 | 1 |
| 14 | 4 | 7 | 1 |
If input is these two emails:
Kanchhi#example.com, john#example.com
Then my expected expected output is this (order does not matter):
andy#example.com
jetli#example.com
In the above example, the friends of user id 2 is user ids (4, 6, 7) and friend of user id 7 is user ids (2, 4, 5, 6). So the mutual friend of user id 2 and 7 is 4 and 6. I need email address of mutual user id.
Another example input is:
andy#example.com, john#example.com
Then expected output is this:
jetli#example.com
Kanchhi#example.com
maya#example.com`
In the above example, friend of user id 4 is (2, 6, 5, 3, 2) and friend of user id 7 is (6, 5, 2, 4). So mutual friend user id will be 2, 6, 5. I need email address of these user id in output.
Query 1- I tried but got wrong result:
SELECT u.email
FROM user_relations r
LEFT JOIN users u ON r.requestor_user_id = u.user_id
LEFT JOIN users z ON r.receiver_user_id = z.user_id
where u.email in ('Kanchhi#example.com','john#example.com') or
z.email in ('Kanchhi#example.com','john#example.com')
and r.friend_status = 1
group by u.email
having count(u.email ) > 1
Results- but not correc:
| email |
|---------------------|
| andy#example.com |
| john#example.com |
| Kanchhi#example.com |
How to get this?

Answer 1

The crux of the problem is building a list of users that are friends of Kanchi and John or have them as friends. Then count those users that appear in the list twice:
-- SELECT email FROM users WHERE userid IN (
SELECT friendid
FROM (
SELECT requestor_user_id AS userid, receiver_user_id AS friendid
FROM user_relations
WHERE friend_status = 1 AND requestor_user_id IN (
SELECT user_id
FROM users
WHERE email IN ('Kanchhi#example.com','john#example.com')
)
UNION ALL
SELECT receiver_user_id, requestor_user_id
FROM user_relations
WHERE friend_status = 1 AND receiver_user_id IN (
SELECT user_id
FROM users
WHERE email IN ('Kanchhi#example.com','john#example.com')
)
) AS X
GROUP BY friendid
HAVING COUNT(DISTINCT userid) = 2
Matching the results with users is trivial. For your sample input the result is:
4 Andy andy#example.com ashutosh 2019-01-11 13:34:05
6 jetli jetli#example.com ashutosh 2019-01-11 13:34:05

Answer 2

You can start from the user, then join the relations.
Then group on the receiver & requestor that are different from the user.
SELECT
case when u.user_id = r.receiver_user_id then requestor.email else receiver.email end as friend_email
FROM users u
JOIN user_relations r
ON (r.requestor_user_id = u.user_id OR r.receiver_user_id = u.user_id)
AND r.friend_status = 1
LEFT JOIN users requestor ON requestor.user_id = r.requestor_user_id
LEFT JOIN users receiver ON receiver.user_id = r.receiver_user_id
WHERE u.email in ('Kanchhi#example.com','john#example.com')
GROUP BY friend_email
HAVING COUNT(DISTINCT u.user_id) > 1
Result:
friend_email
----------------
andy#example.com
jetli#example.com

Answer 3

You could use this and use index in join coulmn for performance
SELECT DISTINCT u.email
FROM
(
SELECT r.receiver_user_id AS id, u.email
FROM user_relations r
INNER JOIN users u
ON r.requestor_user_id = u.user_id
WHERE r.friend_status = 1 AND u.email = 'Kanchhi#example.com'
UNION ALL
SELECT r.requestor_user_id AS id, u.email
FROM user_relations r
INNER JOIN users u
ON r.receiver_user_id = u.user_id
WHERE r.friend_status = 1 AND u.email = 'Kanchhi#example.com'
) k
INNER JOIN
(
SELECT r.receiver_user_id AS id, u.email
FROM user_relations r
INNER JOIN users u
ON r.requestor_user_id = u.user_id
WHERE r.friend_status = 1 AND u.email = 'john#example.com'
UNION ALL
SELECT r.requestor_user_id AS id, u.email
FROM user_relations r
INNER JOIN users u
ON r.receiver_user_id = u.user_id
WHERE r.friend_status = 1 AND u.email = 'john#example.com'
) j
ON k.id = j.id
INNER JOIN users u
ON k.id = u.user_id
AND u.email NOT IN ('Kanchhi#example.com','john#example.com');

Answer 4

Try this
SELECT usu.email from users usu where usu.user_id in (
select r.receiver_user_id
from sov.user_relations r
where r.requestor_user_id in (
SELECT u.user_id from users u where u.email in ('Kanchhi#example.com','john#example.com')
)
and r.friend_status = 1
group by r.receiver_user_id
having count(r.receiver_user_id) > 1
);

Answer 5

you can create extra function like below code
BEGIN
DECLARE limitCount INT DEFAULT 0;
DECLARE counter INT DEFAULT 0;
DECLARE res INT DEFAULT 0;
DECLARE temp TEXT;
SET limitCount = 1 + LENGTH(inputList) - LENGTH(REPLACE(inputList, ',',''));
simple_loop:LOOP
SET counter = counter + 1;
SET temp = SUBSTRING_INDEX(SUBSTRING_INDEX(inputList,',',counter),',',-1);
SET res = FIND_IN_SET(temp,targetList);
IF res > 0 THEN LEAVE simple_loop; END IF;
IF counter = limitCount THEN LEAVE simple_loop; END IF;
END LOOP simple_loop;
RETURN res;
END
AND USE THIS FUNCTION LIKE THIS
find_in_set_extra('Kanchhi#example.com, john#example.com','john#example.com') OR WHAT EVER YOUR INPUTS AND OUTPUTS.