错误信息

Db Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') ORDER BY add_times desc LIMIT 0,20' at line 1
SELECT obj_news.*,obj_news_cls.cls_name,obj_news_cls.cls_pic,obj_news_cls.cls_desc,obj_news_cls.level FROM `33hao_obj_news` AS `obj_news` LEFT JOIN `33hao_obj_news_cls` AS `obj_news_cls` ON obj_news.cls_id = obj_news_cls.id WHERE obj_news.obj_id = 122 and obj_news.cls_id in () ORDER BY add_times desc LIMIT 0,20