Programming a friends list feature - php

Question

I'd like to firstly point that I'm not very good at advanced MySQL just yet. So please forgive me. What I am trying to do is create a friends list like what's in the image below:
Here is my db structure:
friends table:
users table:
Here is my code so far:
<?php $query3 = $this->db->query("SELECT * FROM friends WHERE node1id = '{$myuserid}'");
foreach($query3->result() as $row1) {
echo $row1->node1id."<br>"; } ?>
I know this code isn't logically correct. What I am trying to do is pull in the users table. And if relationType = friends, display firstname and lastname of the user in the friends list. I have two variables. $selectedId and $myuserid. $selectedId is the id of the profile the user is viewing. and $myuserid is the id of the logged in user. How would I code this type of feature logically?

Answer 1

SELECT username FROM users
WHERE userid IN
(SELECT node2id FROM friends WHERE node1id = '{$myuserid}'
AND relationType = 'friends')
and
echo $row1->username
For mutual friends you could do this
EDIT: Just realised last version of this wasn't right, fixed now (untested)
SELECT username FROM users
WHERE userid IN
(SELECT node2id FROM (
(SELECT node2id FROM friends WHERE relationType = 'friends' AND node1id <> '{$myuserid}' AND node1id IN
(SELECT node2id FROM friends WHERE relationType = 'friends' AND node1id = '{$myuserid}')))
WHERE node2id IN (SELECT node2id FROM friends WHERE relationType = 'friends' AND node1id = '{$myuserid}'))
This first selects friends, then it selects the friends of those friends which is not equal (not equal is <>) to yourself. It then only selects from that list the friendIDs which match your your own friend IDs. It then selects the name of these users from the users table.

Answer 2

You can do a select inside of a select like below:
SELECT * FROM users WHERE idusers IN (
SELECT node2id FROM friends WHERE node1id = $myUserId
)

Answer 3

Here's how to get all friends of a particular user ($selectedid), and determine whether or not each of their friend is a mutual friend:
SELECT b.*,
c.myfrnd IS NOT NULL AS isMutual
FROM (
SELECT IF(node2id = '$selectedid', node1id, node2id) AS usrfrnd
FROM friends
WHERE '$selectedid' IN (node1id,node2id) AND
relationType = 'friends'
) a
JOIN users b ON a.usrfrnd = b.userid
LEFT JOIN (
SELECT IF(node2id = '$myuserid', node1id, node2id) AS myfrnd
FROM friends
WHERE '$myuserid' IN (node1id,node2id) AND
relationType = 'friends'
) c ON b.userid = c.myfrnd
ORDER BY isMutual DESC
The column isMutual will contain 1 if the friend is a mutual friend, otherwise 0 if not. Mutual friends show up first in the result set.
The thing you have to consider is that a user could be in either columns node1id or node2id, so in order to get a consistent join, we use a subselect to force the friends of the parameter userids ($selectedid and $myuserid) to be in the same column.
Let me know how this works.