我如何“命令”加入SQL查询？

Question

这有效......

$sql30 = "SELECT * FROM statuses LEFT JOIN friends ON statuses.userID=friends.lowerFriendID WHERE friends.lowerFriendID != :user_ida
    UNION SELECT * FROM statuses RIGHT JOIN friends ON statuses.userID=friends.higherFriendID WHERE friends.higherFriendID != :user_idb ORDER BY userID DESC";

但我不需要按userID排序，这不起作用......

$sql30 = "SELECT * FROM statuses LEFT JOIN friends ON statuses.userID=friends.lowerFriendID WHERE friends.lowerFriendID != :user_ida
    UNION SELECT * FROM statuses RIGHT JOIN friends ON statuses.userID=friends.higherFriendID WHERE friends.higherFriendID != :user_idb ORDER BY id DESC";

也不是......

$sql30 = "SELECT * FROM statuses LEFT JOIN friends ON statuses.userID=friends.lowerFriendID WHERE friends.lowerFriendID != :user_ida
    UNION SELECT * FROM statuses RIGHT JOIN friends ON statuses.userID=friends.higherFriendID WHERE friends.higherFriendID != :user_idb ORDER BY `id` DESC";

也不是......

$sql30 = "SELECT * FROM statuses LEFT JOIN friends ON statuses.userID=friends.lowerFriendID WHERE friends.lowerFriendID != :user_ida
    UNION SELECT * FROM statuses RIGHT JOIN friends ON statuses.userID=friends.higherFriendID WHERE friends.higherFriendID != :user_idb ORDER BY timestamp DESC";

我需要通过“id”或“timestamp”DESC进行排序，以便最新的帖子首先显示。非常感谢您的帮助。谢谢！