Friends of Friends query for 1 way relationships - mysql

Question

This is my table: (friends)
user_id
friend_id
1
2
1
3
1
4
2
1
2
5
3
7
3
8
4
1
4
5
9
2
10
1
11
8
11
7
The table contains 1 way relationship. For eg. User 1 is following User 3, but User 3 is not following User 1.
So Each user has Followers and Following data.
What I want in my output is:
Get Followers of selected user + followers and following of those Followers
Plus (+)
Get Followings of selected user + followers and following of those Followings
Desired Output:-
user_id
friend_id
1
2
1
3
1
4
2
1
2
5
3
7
3
8
4
1
4
5
9
2
10
1
This is my current query:
SELECT t1.*
FROM friends t1
JOIN friends t2 ON t1.friend_id=t2.user_id
WHERE t2.friend_id=$user_id
UNION
SELECT t1.*
FROM friends t1
JOIN friends t2 ON t1.friend_id=t2.friend_id
WHERE t2.friend_id=$user_id
;
I got this query from here: How to get friends of friends of friends... (#Adams answer)
But I don't think it is looping through all the condition that I want in my case. Any help would be much appreciated, thanks.
Edit:- #sajjad rezaei answer satisfies all the conditions, but is not exactly the output that I wanted.
(my bad, I should have added my desired output.)
Here is the dbfiddle link of the output:- https://www.db-fiddle.com/f/sWVYZKVWMbbEUkShJmje2Q/5

Answer 1

With this query:
SELECT CASE WHEN user_id = 1 THEN friend_id ELSE user_id END id
FROM friends
WHERE 1 IN (user_id, friend_id);
you get all the followers and followings of user = 1.
Join it to the table:
SELECT DISTINCT f.user_id, f.friend_id
FROM friends f
INNER JOIN (
SELECT CASE WHEN user_id = 1 THEN friend_id ELSE user_id END id
FROM friends
WHERE 1 IN (user_id, friend_id)
) t ON t.id IN (f.user_id, f.friend_id)
ORDER BY f.user_id, f.friend_id;
See the demo.

Answer 2

The fiddle
Here's one for MySQL 5.7 (8.0 or less):
SELECT user_id, friend_id
FROM (
SELECT f.user_id, f.friend_id FROM friends AS f WHERE 1 IN (f.user_id, f.friend_id) UNION
SELECT f.user_id, f.friend_id
FROM (
SELECT f.user_id, f.friend_id FROM friends AS f WHERE 1 IN (f.user_id, f.friend_id)
) AS f0
JOIN friends AS f
ON f0.user_id IN (f.friend_id, f.user_id)
OR f0.friend_id IN (f.friend_id, f.user_id)
) AS fof
ORDER BY user_id, friend_id
;
Here's one for MySQL 8.0+:
WITH RECURSIVE fof (user_id, friend_id, n) AS (
SELECT f.user_id, f.friend_id, 1 FROM friends AS f WHERE 1 IN (f.user_id, f.friend_id) UNION ALL
SELECT f.user_id, f.friend_id, n+1
FROM friends AS f
JOIN fof AS f2
ON ( f.user_id IN (f2.friend_id, f2.user_id)
OR f.friend_id IN (f2.friend_id, f2.user_id)
)
AND n < 2
)
SELECT DISTINCT user_id, friend_id
FROM fof
ORDER BY user_id, friend_id
;
The result:
user_id
friend_id
1
2
1
3
1
4
2
1
2
5
3
7
3
8
4
1
4
5
9
2
10
1
I used the following to count the larger data set...
Non-recursive:
SELECT COUNT(*)
FROM (
SELECT f.user_id, f.friend_id FROM friends AS f WHERE 1066 IN (f.user_id, f.friend_id) UNION
SELECT f.user_id, f.friend_id
FROM (
SELECT f.user_id, f.friend_id FROM friends AS f WHERE 1066 IN (f.user_id, f.friend_id)
) AS f0
JOIN friends AS f
ON f0.user_id IN (f.friend_id, f.user_id)
OR f0.friend_id IN (f.friend_id, f.user_id)
) AS fof
;
Recursive:
WITH RECURSIVE fof (user_id, friend_id, n) AS (
SELECT f.user_id, f.friend_id, 1 FROM friends AS f WHERE 1066 IN (f.user_id, f.friend_id) UNION ALL
SELECT f.user_id, f.friend_id, n+1
FROM friends AS f
JOIN fof AS f2
ON ( f.user_id IN (f2.friend_id, f2.user_id)
OR f.friend_id IN (f2.friend_id, f2.user_id)
)
AND n < 2
)
, xxx AS (
SELECT DISTINCT user_id, friend_id
FROM fof
ORDER BY user_id, friend_id
)
SELECT COUNT(*) FROM xxx
;
The result:
+----------+
| COUNT(*) |
+----------+
| 12125 |
+----------+

Answer 3

It might help you with your situation:
(SELECT f1.* ,
(SELECT GROUP_CONCAT(friend_id) from friends WHERE user_id = f1.friend_id) AS followerOFfollowers,
(SELECT GROUP_CONCAT(user_id) from friends WHERE friend_id = f1.friend_id) AS followingOFfollowers
FROM friends as f1
WHERE f1.user_id = 1 GROUP by f1.id , f1.friend_id)
UNION
(SELECT f1.* ,
(SELECT GROUP_CONCAT(friend_id) from friends WHERE user_id = f1.user_id) AS followerOFfollowers,
(SELECT GROUP_CONCAT(user_id) from friends WHERE friend_id = f1.user_id) AS followingOFfollowers
FROM friends as f1
WHERE f1.friend_id = 1 GROUP by f1.id , f1.user_id)