php - 共同好友查询

Question

我正在尝试创建一个共同好友查询。但我不确定如何合并两个表以获得正确的结果。

因此，如果 session 用户与他们的 friend 有共同的 friend ，那么共同的 friend 就是其中之一。我正在寻找的是完成这项工作的最佳解决方案、最快和最小的查询。

用户表

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

friend 表

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

尝试查询

 $collectmutualfriends = mysqli_query($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>";
    }

更新

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

$user1_id 和 $user2_id 可以在好友表的 user1_id 或 user2_id 中，具体取决于谁先发送了好友请求。

Answer 1

这应该可以解决问题:

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