php数组加循环，我这样写错在哪里？

Question

        $list = array ();
        $query = $this->db->query ( "SELECT id FROM table where cid = 1" );
        foreach ( $query->result_array () as $idlist ) {
            $list [] = $idlist;
        }

        $count = count ( $list );
        for($i = 0; $i < $count; $i ++) {
           $num = $list[$i];
           $this->db->query ( "UPDATE category SET zong=XXXX where id =$num " ）；
        }

我是想先查询出所有的id，循环执行更新sql语句，条件where根据上面查询的结果id循环执行

Answer 1

    foreach ( $query->result_array () as $idlist ) {
        $list [] = $idlist;
    }

这里不对
直接写
foreach ( $query->result_array () as $idlist ) {
$this->db->query ( "UPDATE category SET zong=XXXX where id =" + $idlist ）
}