JQuery DataTables默认排序无效

我的数据表默认排序由于某些我无法弄清楚的原因而无法正常工作.但数据显示正确.分页也不起作用.第一列包含图像,但我将其设置为默认不执行任何排序.

任何帮助都非常感谢.

这是我正在使用的代码的一部分:

var oTable = $('#datatables').dataTable( {
        "aaSorting": [[2, 'asc']],
        "bProcessing": true,
        "bServerSide": true,
        "sPaginationType": "full_numbers",
        "sAjaxSource": "process.php",
        "aoColumns": [
            {
                "mData": null,
                "aTargets": [0],
                "bSerchable": false,
                "bSortable": false,
                "sDefaultContent": '
',
                "sWidth": "30px"
            },
            { 
                "mDataProp": "email",
                "aTargets": [1],
                "bSearchable": true,
                "bSortable": true
            },
            { 
                "mDataProp": "lastName",
                "aTargets": [2],
                "bSearchable": true,
                "bSortable": true
            },
            { 
                "mDataProp": "firstName",
                "aTargets": [3],
                "bSearchable": true,
                "bSortable": true
            },
            { 
                "mDataProp": "dateRegistered",
                "aTargets": [4],
                "sClass": "center",
                "bSearchable": true,
                "bSortable": true
            }
        ]
    } );

我刚刚添加了"aTargets",与没有它们的情况一样.

这是返回json数组的文件:

prepare($sql) or die ($sql);

            if(!$result->execute()) return false;

            if($result->rowCount() > 0) {
                $json = array();
                while($row = $result->fetch()){
                    $json[] = array(
                        'email' => $row['email'],
                        'lastName' => $row['lastName'],
                        'firstName' => $row['firstName'],
                        'dateRegistered' => $row['dateRegistered'],
                        'state' => $row['state']
                    );
                }

                $response = array(
                    "iTotalRecords" => strval(count($json)),
                    "iTotalDisplayRecords" => strval(count($json)),
                    "aaData" => $json
                );

                echo json_encode($response);

            }
        } catch(PDOException $e) {
            echo 'Error: ' . $e->getMessage();
        }

?>

谢谢.