Finding friends of a user - mysql

Question

I have a table of user with differents fields : id, firstname, name.
I have a table called friend with differents fields : invite_id, friend_sender (id of a user), friend_receiver (id of a user), validity (boolean).
I'm filling the friend table with
1, 1, 2, 0;
2, 3, 1, 1;
3, 1, 5, 1;
Let's imagine I'm user 1, and I want to find all my friends. I can be the one who sent the friend invitation (sender), or the one who received it (receiver). When the receiver accept the invitation, the validity of the relation is set to 1. So for example, I'm not friend with user 2 because he didn't accepted.
The result I should get from doing the query with user 1 should be :
3, firstnameofuser3, nameofuser3
5, firstnameofuser3, nameofuser3
I tried some SQL things, with double JOIN, renaming table to avoid the "double same table" problems etc ... but I couldn't figure it out.
I've found some post about it, but for more complex things, like here :
Finding mutual friend sql
Thank you in advance for you help.

Answer 1

I know there are already answers, but mine is unique AND I have a fiddle! ;)
SELECT
id,
firstname,
name
FROM
user
WHERE id IN
(
SELECT
CASE WHEN friend_sender = 1 THEN friend_receiver ELSE friend_sender END
FROM friend
WHERE
(friend_sender = 1 OR friend_receiver = 1)
AND
validity = 1
)
Fiddle: http://sqlfiddle.com/#!9/d8f55a/1

Answer 2

Try this:
SELECT u.*
FROM user u
WHERE u.id IN (
SELECT f.friend_sender
FROM friend f
WHERE f.friend_receiver = 2 -- My fixed ID about Jin Jey
UNION
SELECT f.friend_receiver
FROM friend f
WHERE f.friend_sender = 2 AND f.validity = 1)
I used UNION because you can query two sets of data and merge it.
I fixed ID (2) because in your request you want to know all friends about Jin Jey

Answer 3

You can try the below query
select
id,
firstname,
name
from
user inner join friend
on
(friend_sender=1 or friend_receiver=1 )and validity=1
and
user.id=
(case
when friend_sender=1 then friend_receiver
else friend_sender
end)
demo link here