Friends of a user + mutual friend test with another user - mysql

Question

I have this table that I use (but not only) for storing friends in a database :
user_1 | user_2 | status
where 'status' can be -1,0 or 1. Here, we will consider only cases where status are '0' (pending for user_1) or '1' (approved by user_2). I have the following query to look for pending/approved friends for a given $user :
SELECT user_1,user_2,status
FROM Friends
WHERE (user_2 = '$user' OR user_1 = '$user') AND status >= 0;
The goal here is to modify the query to also tell if a given $user2 is a common (approved) friend of $user1 and each (approved) friend of $user1.
After some researches, I figured out that the left join would do the trick, by setting another field to either NULL (if no mutual) or $user2. I would want to do it efficiently. I tried several shots, but no success around it.
Thanks by advance for your help
EDIT : For example, let's say we have the following entries :
a | b | 1
c | a | 1
c | b | 1
a | d | 1
I want to list the friends of 'a' and for each friend f of 'a', verify if 'b' is a common friend of f and 'a'. Also, f =/= b for the mutual test. The result of such a query would be :
a | b | 1 | NULL
c | a | 1 | b
a | d | 1 | NULL
Let me know if you need more clarification

Answer 1

As in MySQL query would be so complicated and slow, that I wouldn't use it myself, here's a solution in PHP, with only one query:
<?php
// $db = mysqli_connect(...);
function findMutualFriends($of,$mutual_with){
global $db;
$user_friends = array();
$mutual_friends = array();
$results = array();
$res = mysqli_query($db,"SELECT user_1,user_2,status FROM Friends WHERE ((user_2 = '$of' OR user_1 = '$of') OR (user_2 = '$mutual_with' OR user_1 = '$mutual_with')) AND status >= 0;";
while($row = mysqli_fetch_assoc($res)){
if($row['user_1'] == $of || $row['user_2'] == $of){
$user_friends[] = (($row['user_1'] == $of) ? $row['user_2'] : $row['user_1']);
}
if($row['user_1'] == $mutual_with || $row['user_2'] == $mutual_with){
$mutual_friends[(($row['user_1'] == $mutual_with) ? $row['user_2'] : $row['user_1'])] = 1;
}
}
foreach($user_friends as $friend){
if($mutual_firends[$friend]){
$results[] = $friend;
}
}
return $results;
}
?>
Please notice that it haven't been tested. May contain some minor syntax error, but should return an array of mutual friends.

Answer 2

I modified a bit the Flash Thunder's function post. Just tested with some modifications and it works ! Thanks again.
function findMutualFriends($pdo, $of,$mutual_with){
$user_friends = array();
$mutual_friends = array();
$results = array();
$query = "SELECT user_1,user_2,status FROM Friends WHERE ((user_2 = '$of' OR user_1 = '$of') OR (user_2 = '$mutual_with' OR user_1 = '$mutual_with')) AND status = 1;";
$prep = $pdo->prepare($query);
$res = $prep->execute();
$rows = $prep->fetchAll();
foreach ($rows as $row) {
if($row['user_1'] == $of || $row['user_2'] == $of) {
$user_friends[] = ($row['user_1'] == $of ? $row['user_2'] :$row['user_1']);
}
if($row['user_1'] == $mutual_with || $row['user_2'] == $mutual_with) {
$mutual_friends[($row['user_1'] == $mutual_with ? $row['user_2'] :$row['user_1'])] = true;
}
}
foreach($user_friends as $friend) {
$results[$friend] = $mutual_friends[$friend] == true ? true : false;
}
return $results;
}