编程好友列表功能

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.