display subcategory after a specific category is selected

[learner001]

I have a form that has two parameters amenities and attributes. The amenities parameter has a dropdown menu that whose value gets populated from a separate table. The second parameter is attribute whose value will be entered by the user and will get saved in a database. View of database will be:

ID  Attribute  Amenities
1     A          Aa
2     B          Bb

Code for this part is

<form class="form-horizontal" role="form" action="admin_insert_attribute.php" enctype="multipart/form-data" method="post">    
    <div class="form-group">
        <label class="col-lg-3 control-label">Amenities:</label>
            <div class="col-lg-8">    
                <?php
                    $con=mysqli_connect("abc","abc","abc","abc");
                    // Check connection
                    if (mysqli_connect_errno()) 
                    {
                    echo "Failed to connect to MySQL: " . mysqli_connect_error();
                    }

                    $result = mysqli_query($con,"SELECT amenities FROM amenities");
                    echo "<select name='amenities'>";
                    while($row = mysqli_fetch_array($result)) 
                    {
                    echo "<option value='" . $row['amenities'] . "'>" . $row['amenities'] . "</option>";
                    }   
                    echo "</select>";   
                    mysqli_close($con);
                ?>  
            </div>
    </div>    
    <div class="form-group">
        <label class="col-lg-3 control-label">Attribute:</label>
            <div class="col-lg-8">
                <input class="form-control" name="attribute" value="" type="" required>
            </div>
    </div>

    <div class="form-group">
        <label class="col-lg-3 control-label"></label>
            <div class="submit">
             <input class="btn btn-primary" value="Save " type="submit" name="submit">    
            </div>  
    </div>
</form>

Now I wish that when an amenity is selected from the dropdown menu all the attribute under that specific amenity should also get displayed on the same page in a tabular form. Code for entering and displaying the attribute is done on the same page.

Problem is that i am able to add the attributes but they are not getting displayed on the screen. Code that i used for displaying is

<?php
    $con=mysqli_connect("abc","abc","abc","abc");
    // Check connection
    if (mysqli_connect_errno()) 
        {
            echo "Failed to connect to MySQL: " . mysqli_connect_error();
        }

    $result = mysqli_query($con,"SELECT * FROM attributes  WHERE amenities = '".$amenities."'");
    echo "<table class='table table-striped table-bordered table-hover'>
        <thead>
            <tr>
                <th>ID</th>
                <th>Attribute</th>
            </tr>
        </thead>";

    while($row = mysqli_fetch_array($result)) 
        {
            echo "<tbody data-link='row' class='rowlink'>";
            echo "<tr>";
            echo "<td>" . $row['id'] . "</td>";
            echo "<td>" . $row['attribute'] . "</td>";      
            echo "</tr>";
            echo "</tbody>";    
        }
    echo "</table>";
    mysqli_close($con);
?>

[pritaeas]

they are not getting displayed on the screen

Where is the javascript code that is adding the output of the script to your page?