此SQL用来删除同一表中，不是互为好友的朋友ID，比如我加了你，你没有加我，那么从我的表中删除你的ID
mysql> DELETE FROM zt_user_friends_info WHERE zt_friend_id NOT IN (SELECT zt_friend_id from (SELECT A.zt_friend_id FROM zt_user_friends_info A INNER JOIN zt_user_friends_info B ON A.zt_user_id = B.zt_friend_id AND A.zt_friend_id = B.zt_user_id where A.zt_user_id=10580) AA) and zt_user_id=10580;