PHP选择下拉[关闭]

I am trying to make a form with several drop downs for selecting location in the world.

<div class="form-group control-group">
                    <label for="text" class="col-sm-2 control-label">Country</label>
                    <div class="col-sm-8">
                        <select class="form-control">
                            <option>1</option>
                            <option>2</option>
                            <option>3</option>
                            <option>4</option>
                            <option>5</option>
                        </select>
                    </div>
                </div>

                <div class="form-group control-group">
                    <label for="text" class="col-sm-2 control-label">State/Province</label>
                    <div class="col-sm-8">
                        <select class="form-control">
                            <option>1</option>
                            <option>2</option>
                            <option>3</option>
                            <option>4</option>
                            <option>5</option>
                        </select>
                    </div>
                </div>

                <div class="form-group control-group">
                    <label for="text" class="col-sm-2 control-label">City</label>
                    <div class="col-sm-8">
                        <select class="form-control">
                            <option>1</option>
                            <option>2</option>
                            <option>3</option>
                            <option>4</option>
                            <option>5</option>
                        </select>
                    </div>
                </div>

                <div class="form-group control-group">
                    <label for="text" class="col-sm-2 control-label">Postal Code</label>
                    <div class="col-sm-8">
                        <input type="text" class="form-control" id="subject" name="subject">
                    </div>
                </div>

I want to display only the country list if country is not selected and country and state/province list if country is selected... so on. The list will be stored in SQL.

Any help is appreciated. Thanks.

<select id="country" class="form-control" onchange="javascript:countryChange();">
    <option>1</option>
    <option>2</option>
</select>

<select id="state" class="form-control" onchange="javascript:stateChange();">
</select>

<select id="city" class="form-control"></select>

<script>
function countryChange() {
    var selected = jQuery("#country option:selected").text();

    jQuery.ajax({
        url: "country2states.php?country="+selected
    }).done(function(msg) {
        jQuery("#state").html('');
        jQuery("#city").html('');
        jQuery("#state").html(msg);
    });
}

function stateChange() {
    var selected = jQuery("#state option:selected").text();

    jQuery.ajax({
        url: "state2cities.php?state="+selected
    }).done(function(msg) {
        jQuery("#city").html('');
        jQuery("#city").html(msg);
    });
}
</script>

For the first function to work, you have to create a PHP page (country2states.php) to handle the database query to retrieve the list of states for the selected country

"SELECT statename FROM states WHERE country='" . $_GET['country'] . "';"

and return it ECHOing a string formatted like this:

"<option>Iowa</option><option>South Dakota</option><option>Texas</option>....."

Same stuff for the second function, you will create state2cities.php and you know the rest. :)