/home/hdwebsolution/www/ns-interior/admin-pages/get-subcategories.php
<?php
include('../connection.php');

if (isset($_GET['cat_id']) && is_numeric($_GET['cat_id'])) {
    $cat_id = intval($_GET['cat_id']);
    $sql = mysqli_query($link, "SELECT * FROM tbl_sub_category WHERE category_id = $cat_id ORDER BY name ASC");

    echo "<option value=''>-- Select Sub Category --</option>";
    while ($row = mysqli_fetch_assoc($sql)) {
        echo "<option value='{$row['id']}'>{$row['name']}</option>";
    }
}
?>