准备语句以检查关注者是否尚未关注关注者？

如何解决准备语句以检查关注者是否尚未关注关注者？

我需要检查MysqL数据库以查看关注者是否已关注关注者。但是我不确定该怎么做。我猜我应该使用IF语句。这是我到目前为止所管理的；

<?PHP

header('Cache-Control: no-cache,must-revalidate');
include 'pdo.PHP';

$userid = $_POST['userid'];
$currentuserid = $_POST['currentuserid'];

$checkexist = "SELECT follower,followee FROM follow WHERE followee = :userid";
$checkvalues = [':userid' => $userid];

$query = "INSERT INTO follow (followee,follower) VALUES(:followee,:follower)";
$values = [':followee' => $userid,':follower' => $currentuserid];

try {
    $stmt = $pdo->prepare($checkexist);
    $stmt->execute($checkvalues);
    $rows = $stmt->fetchall(PDO::FETCH_ASSOC);

    foreach ($rows as $row) {
        if ($row->followee != $currentuserid) {
            if ($row->follower != $userid) {
                $res = $pdo->prepare($query);
                $res->execute($values);
                echo "Successfully followed user";
            }
        } else {
            echo "You can't follow yourself";
        }
    }
} catch (PDOException $e) {
    echo 'Error following user';
    die();
}

我真正想做的是；

首先，检查跟随者是否在试图跟随自己（被跟随者）。

然后检查关注者是否尚未关注关注者。

最后在跟随者之后的跟随者中插入一条记录。