如何在DataTables上只显示前N行？在此之后如何下载所有数据？

$(document).ready(function() {
    $('#myTable').DataTable({
        "pageLength": N
    });
});

<link rel="stylesheet" type="text/css" href="https://cdn.datatables.net/1.11.3/css/jquery.dataTables.min.css">
<link rel="stylesheet" type="text/css" href="https://cdn.datatables.net/buttons/2.0.1/css/buttons.dataTables.min.css">

<script type="text/javascript" src="https://cdn.datatables.net/1.11.3/js/jquery.dataTables.min.js"></script>
<script type="text/javascript" src="https://cdn.datatables.net/buttons/2.0.1/js/dataTables.buttons.min.js"></script>
<script type="text/javascript" src="https://cdn.datatables.net/buttons/2.0.1/js/buttons.html5.min.js"></script>

$(document).ready(function() {
    var table = $('#myTable').DataTable({
        "pageLength": N,
        "buttons": [
            'excelHtml5'
        ]
    });

    table.buttons().container()
        .appendTo('#myTable_wrapper .dataTables_filter'); // 将按钮添加到搜索框的旁边
});