Php 如何仅从friend_阵列上的用户获取帖子？

我只想查看我朋友的帖子，但我得到的是所有用户的帖子。我不想在我的查询中为friend_数组使用单独的表

以下是我的帖子示例数据：

id  body    date_added  added_by    user_posted_to
1   whats up 2015-09-12 Francis     2pac
2   update  2015-09-12  Cate        Cate
3   my life 2015-09-12  Cate        2pac

id  username first_name last_name email password sign_up_date   activated   bio     profile_pic     friend_array    closed
1   Paul    Paul   Kent     paul@yahoo.com   894416aea718e7c44a126581dd017588    2015-08-18  0   hello   C2LTjo79O4I63Gt/004.jpg     Cate,Mike,Grace    Yes               
2   Christine    Christine     Monica    monica@gmail.com  894416aea718e7c44a126581dd017588    2015-08-18  0   welcome     3mlbDJSXoThHvEi/023.jpg     Paul,Andrew,Jacob     no

以下是我的用户示例数据：

id  body    date_added  added_by    user_posted_to
1   whats up 2015-09-12 Francis     2pac
2   update  2015-09-12  Cate        Cate
3   my life 2015-09-12  Cate        2pac

id  username first_name last_name email password sign_up_date   activated   bio     profile_pic     friend_array    closed
1   Paul    Paul   Kent     paul@yahoo.com   894416aea718e7c44a126581dd017588    2015-08-18  0   hello   C2LTjo79O4I63Gt/004.jpg     Cate,Mike,Grace    Yes               
2   Christine    Christine     Monica    monica@gmail.com  894416aea718e7c44a126581dd017588    2015-08-18  0   welcome     3mlbDJSXoThHvEi/023.jpg     Paul,Andrew,Jacob     no

这是我的密码：

//If the user is logged in
$getposts = $mysqli->query("
SELECT * FROM posts 
INNER JOIN users 
ON FIND_IN_SET(posts.added_by, users.friend_array) 
ORDER BY date_added DESC LIMIT 100") 
or die(mysqli_error($mysqli)); 

while ($row = mysqli_fetch_assoc($getposts)) {
                    $id = $row['id'];
                    $body = $row['body'];    
                    $date_added = $row['date_added'];
                    $added_by = $row['added_by'];
                    $user_posted_to = $row['user_posted_to'];