如何在Jquery Datatable底部添加合计单元

<table id="myTable">
  <thead>
    <tr>
      <th>列1</th>
      <th>列2</th>
      <th>列3</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>数据1</td>
      <td>数据2</td>
      <td>数据3</td>
    </tr>
    <!-- 其他数据行 -->
  </tbody>
</table>

$(document).ready(function() {
  $('#myTable').DataTable({
    "footerCallback": function (row, data, start, end, display) {
      var api = this.api();
      $(api.column(0).footer()).html('合计');
      // 计算每列的合计值
      var column1Total = api.column(1, {page: 'current'}).data().sum();
      var column2Total = api.column(2, {page: 'current'}).data().sum();
      // 在底部合计行显示合计值
      $(api.column(1).footer()).html(column1Total);
      $(api.column(2).footer()).html(column2Total);
    }
  });
});

$.fn.dataTable.Api.register( 'sum()', function () {
    return this.flatten().reduce( function ( a, b ) {
        if ( typeof a === 'string' ) {
            a = a.replace(/[^\d.-]/g, '') * 1;
        }
        if ( typeof b === 'string' ) {
            b = b.replace(/[^\d.-]/g, '') * 1;
        }
        return a + b;
    }, 0 );
} );