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_pro.*,obj_pro_cls.cls_name,obj_pro_cls.cls_pic,obj_pro_cls.cls_desc,obj_pro_cls.level FROM `33hao_obj_pro` AS `obj_pro` LEFT JOIN `33hao_obj_pro_cls` AS `obj_pro_cls` ON obj_pro.pro_cls_id=obj_pro_cls.id WHERE obj_pro.obj_id = 122 and obj_pro.is_show = 1 and obj_pro.pro_cls_id in () ORDER BY add_times desc LIMIT 0,20