php - 试图弄清楚 MySQL 查询的作用(不是我的)

Question

我有以下可能与此查询相关的 MySQL 表:

Table: user_follow
Columns:   |  Type:
-----------|---------
id         |  INT(11)
follower   |  INT(11)
user       |  INT(11)
subscribed |  INT(11)

ID是关注者的ID，关注者是关注用户的人，订阅是关注用户的时间。关注者和用户将是用户表中人员的 ID:

Table: users
Columns:  |  Type:
----------|---------
id        |  INT(11)
username  |  INT(11)

这不是完整的用户表，但是对于此 MySQL 查询正在执行的任何操作来说，这应该足够了。 users表中的ID是用户的ID，username是用户名。所以这是我试图弄清楚它在做什么的查询。我相信它正在尝试从用户的数据库中获取用户名:

SELECT `ufollower`.`id` AS follower_id, `ufollower`.`username` AS follower_name,
     `ufollowed`.`id` AS user_id, `ufollowed`.`username` AS user_name
FROM `user_follow`
JOIN users ufollower ON `ufollower`.`id` = `user_follow`.`follower`
JOIN users ufollowed ON `ufollowed`.`id` = `user_follow`.`user`
WHERE `user_follow`.`user` = :p_id

我尝试运行的完整代码是这样的(包括查询):

//Get people who this person is following
$following = $db->prepare("SELECT `ufollower`.`id` AS follower_id, `ufollower`.`username` AS follower_name, `ufollowed`.`id` AS user_id, `ufollowed`.`username` AS user_name FROM `user_follow` JOIN users ufollower ON `ufollower`.`id` = `user_follow`.`follower` JOIN users ufollowed ON `ufollowed`.`id` = `user_follow`.`user` WHERE `user_follow`.`user` = :p_id");
$following->bindValue(":p_id",$p_id,PDO::PARAM_STR);
$following->execute();
$following = $following->fetchAll(PDO::FETCH_ASSOC);
var_dump($following);

//If I do $following = $following->fetch(); and var_dump that, it returns "bool(false)" which I learned the other day that it couldn't do the query or there were no results found or something

另外，我不是 MySQL 专家，所以如果您能提供一个也可能有效的答案，那就太好了。我可以做简单的查询，但是当涉及到连接表时，我不知道发生了什么。

Answer 1

基本上，user_follow 表连接另外两个用户，其中一个用户关注另一个用户，并且此查询获取这两个用户的一个特定关注。

这个查询的解释可以描述为:
对于 id :id 的 user_follow 获取正在关注另一用户 (ufollowing) 的一个用户 (ufollower) 及其 ID 和用户名。