filter and sort for dropdowns

Axi

In my table I have a dropdownlist:

<select>
<option value="">alle</option>
<option value="0">keine</option>
<option value="597720000">Überschreitung</option>
<option value="597720001">Unterschreitung</option>
<option value="597720002">Über-/Unterschreitung</option>
</select>

I can't figure out how to do the search nor how to filter.
I have a filter-footer with textboxes and I want to filter for a value of the optionset. Here is my code how I do this:

$("#tblDataPoints tfoot input, #tblDataPoints tfoot select").on('keyup change', function () {
                _tableDataPoints
                    .column($(this).parent().index() + ':visible')
                    .search(this.value)
                    .draw();
            });

this works for all simple text and also for checkboxes but not for my DropDownList.

Any hints?

thx

©a-x-i