如何选择共同的朋友

Question

请我要选择一个用户的共同朋友，并且$my_id是$_SESSION['user']; 而$user_id是选定的用户。 这是代码：

    <?php

include 'connect.php';

include 'functions.php';

$my_frnds = mysqli_query{$con, "SELECT * FROM friends WHERE one='$my_id' OR two='$my_id'"};
while($my_friends = mysqli_fetch_array($my_frnds)){
    $one = $my_friends['one'];
    $two = $my_friends['two'];

    if($one == $my_id){
        $user == $two;
    } else
        $user == $one;
}

$user_frnds = mysqli_query{$con, "SELECT * FROM friends WHERE one='$user_id' OR two='$user_id'"};
while($user_friends = mysqli_fetch_array($user_frnds)){
    $user_one = $user_friends['one'];
    $user_two = $user_friends['two'];

    if($user_one == $my_id){
        $users == $user_two;
    } else
        $users == $user_one;
}

?>

假设我的朋友是（1、2、3、4、5、6、7），用户朋友是（2、4、6、7、8、9、10），因此共同的朋友是（2、4 ，6，7）我的问题是如何让共同的朋友出去并回荡他们的ID？ 抱歉我弄错了，这是原始编码

Answer 1

如果一个是您的ID，两个是朋友ID：

select * from friends 
inner join (select * from friends where one = $user_id) as temp on temp.two = friends.two
where friends.one = $my_id 

Answer 2

    SELECT * FROM friends AS f1
    INNER JOIN 
    (SELECT * FROM friends WHERE one = $user_id OR two = $user_id) AS f2 
    ON (f1.one = f2.one OR f1.one = f2.two) 
    WHERE f1.one = $my_id OR f1.two = $my_id

希望这可以帮助。