相互朋友查询

Question

I'm trying to create a mutual friends query. But I'm unsure how to merge two tables to get the right result.

So if session user has a friend in common with their friend, mutual friend is one. What I'm looking for is the best solution, fastest and smallest query to do the job.

user table

id | first | last | username
----------------------------

friends table

id | user 1_id | user2_id | status
----------------------------------

Attempted query

 $collectmutualfriends = mysqli_query($mysqli,"
    SELECT 
               user.id,
               user.first,
               user.last,
               user.username
    FROM       user 
    LEFT JOIN friends as friends1
           ON  friends1.user1_id = user.id
           AND friends1.user2_id = '$user2_id'
           AND friends1.status = 2

    LEFT JOIN friends as friends2
           ON  friends2.user2_id = user.id
           AND friends2.user1_id = '$user2_id'
           AND friends2.status = 2

    GROUP BY friends2.user2_id
    ");
$nummutual = mysqli_num_rows($collectmutualfriends);
if($nummutual==1){
    echo"<a href='mutualfriends.php?username=".$_GET['username']."'>".$nummutual." Mutual Friend<br></a>";
    }else if($nummutual>1){
    echo"<a href='mutualfriends.php?username=".$_GET['username']."'>".$nummutual." Mutual Friends<br></a>";
    }

UPDATE

$user1_id = $_SESSION['id'];
$user2_id = $data['id'];

$user1_id and $user2_id can be in either user1_id or user2_id on the friends table dependant on who sent the friend request first.

Answer 1

This should do the trick:

$sql = "SELECT u.*
          FROM friends f1 
    INNER JOIN friends f2 ON (f2.user2_id = f1.user2_id)
    INNER JOIN user u ON (u.id = f2.user2_id)
         WHERE f1.user1_id = '$user1_id'
           AND f2.user1_id = '$user2_id'";