PHP：按母类打印子类别项目组

I must to create a menù that contain a list of subcategory items group by mother category and take these values from product table:

Category

Category

I got this:

<?php
 $query_cat = $db->prepare("SELECT * FROM products GROUP BY category ORDER BY category");
 $query_cat->execute();

 print '<li><strong>'. $category . '</strong></li>'; //Category

 while ($cat_row = $query_cat->fetch()) {  //Subcategory
       print '<li><a href="/category/'. $cat_row['4'] .'">'. $cat_row['4'] .'</a></li>'; 
 }
 ?>

The products table structure is

ID, name, stars, brand, category, priceavg, first-category

How i can get the category name and put in top of the element?

Thanks to all for the help provided.

You can use array_group_by function as below

$query_cat = $db->prepare("SELECT name, category, first_category FROM products ORDER BY category");
$query_cat->execute();

$rows = $query_cat->fetchAll(PDO::FETCH_ASSOC);
$items = array_group_by($rows, 'first_category');

foreach($items as $key => $value) {
    echo '<li><strong>' . $key . '</strong></li>';
    foreach($value as $row) {
        echo '<li><a href="/category/'.$row['category'].'">'.$row['category'].'</a></li>';
    }
}

The array_group_by is a function that groups an array by a key or set of keys shared between all array members. Once you've retrieved your SQL data as an associative array, you can apply the array_group_by function an obtain an array of array such as categories and subcategories.

After the array_group_by this is a sample result of how your $items array is structured https://3v4l.org/5WkDH

Final live example here https://3v4l.org/cg9NN

Tip Why is SELECT * considered harmful? Consider to not use SELECT * FROM in your queries

EDIT If you want compatibility to PHP lower than 5.3, you just have to change [] with array() short array notation. Live example here https://3v4l.org/0VUn7 (tested from PHP 4.3 to latest)