você pode criar um arquivo PHP com a solicitação e chamá-lo com AJAX.
getSubCategory.php
<?php
$category = "";
if(isset($_GET['category'])){
$category = $_GET['category'];
}
/* Connect to the database, I'm using PDO but you could use mysqli */
$dsn = 'mysql:dbname=my_database;host=127.0.0.1';
$user = 'my_user';
$password = 'my_pass';
try {
$dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
echo 'Connection failed: ' . $e->getMessage();
}
$sql = 'SELECT sub_category_name as subCategory FROM t_menu_category WHERE category_name = :category';
$stmt = $dbh->prepare($sql);
$stmt->bindValue(':category', $category);
$stmt->execute();
return json_encode($stmt->fetchAll());
e adicione algum jquery para capturar quando uma categoria for selecionada e peça ao servidor a subcategoria correspondente:
<script>
$(document).ready(function () {
$('#item_category').on('change', function () {
//get selected value from category drop down
var category = $(this).val();
//select subcategory drop down
var selectSubCat = $('#item_sub_category');
if ( category != -1 ) {
// ask server for sub-categories
$.getJSON( "getSubCategory.php?category="+category)
.done(function( result) {
// append each sub-category to second drop down
$.each(result, function(item) {
selectSubCat.append($("<option />").val(item.subCategory).text(item.subCategory));
});
// enable sub-category drop down
selectSubCat.prop('disabled', false);
});
} else {
// disable sub-category drop down
selectSubCat.prop('disabled', 'disabled');
}
});
});
</script>
adicione também um valor na sua primeira opção:
<option value="-1" selected="selected">-- Select Category --</option>
