我尝试创建json对象，但无法创建

<?php
 public function get_all_record($table, $fields = \"*\"){

            $sql = \"SELECT $fields FROM $table\";

            $result = $this->sqlordie($sql);

            $xx=0;
            while($row = mysql_fetch_assoc($result))
              {
                $myrow[$xx] = $row;
                $xx++;
              }


             mysql_free_result($result);
             return $myrow;

        }
     private function sqlordie($sql) {

            $return_result = mysql_query($sql, $this->conn);
            if($return_result) {
                return $return_result;
            } else {
                $this->sql_error($sql);
            }
        }

        private function sql_error($sql) {
            echo mysql_error($this->conn).\'<br>\';
            die(\'error: \'. $sql);
        }
?>

 <?php
 $myItem = get_all_record(\"mc_category\",\"category_id,category_name,category_description\");

    echo json_encode($myItem);
?>

[{\"category_id\":\"2\",\"category_name\":\"book\",\"category_description\":\"all type of books\"},{\"category_id\":\"3\",\"category_name\":\"book\",\"category_description\":\"all type of books\"},{\"category_id\":\"4\",\"category_name\":\"Phone\",\"category_description\":\"All type of phones\"},{\"category_id\":\"5\",\"category_name\":\"Phone\",\"category_description\":\"All type of phones\"}]

{ \"aaData\": [
    [\"Trident\",\"Internet Explorer 4.0\",\"Win 95+\",\"4\",\"X\"],
    [\"Trident\",\"Internet Explorer 5.0\",\"Win 95+\",\"5\",\"C\"],
    [\"Trident\",\"Internet Explorer 5.5\",\"Win 95+\",\"5.5\",\"A\"],
    [\"Trident\",\"Internet Explorer 6\",\"Win 98+\",\"6\",\"A\"],
    [\"Trident\",\"Internet Explorer 7\",\"Win XP SP2+\",\"7\",\"A\"]
] }