MySQL server error report:Array ( [0] => Array ( [message] => MySQL Query Error ) [1] => Array ( [sql] => SELECT * from `hk_941in`.`in_article` where is_open = 1 and cat_id in() order by add_time desc LIMIT 9 ) [2] => Array ( [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_time desc LIMIT 9' at line 1 ) [3] => Array ( [errno] => 1064 ) )