Sort items by category - php

Question

I have a table containing the following records:
product_id | title | category
------------------------------------
1 | apple | mobile
2 | android | mobile
3 | dell | desktop
4 | hp | desktop
and the following query:
$sql = "SELECT product_id, title, category FROM products ORDER BY category";
$stmt = $db->prepare($sql);
$stmt->execute();
while($results = $stmt->fetch(PDO::FETCH_ASSOC))
{
echo $results["product_id"];
echo $results["title"];
echo $results["category"];
}
The question is how to split the results and display all records in a list sorted by category as below:
Mobile
Apple
Android
Desktop
Dell
HP

Answer 1

Group your records after get the result set:
$products = array();
while ($results = $stmt->fetch(PDO::FETCH_ASSOC))
{
$products[$results['category']][] = array(
'product_id' => $results['product_id'],
'title' => $results['title']
);
}
foreach ($products as $category => $productList)
{
echo $category . '<br>';
foreach ($productList as $product)
{
echo $product['title'] . '<br>';
}
echo '<hr />';
}

Answer 2

Use SELECT * FROM products GROUP BY category ORDER BY title

Answer 3

After sorting your items (ORDER BY category, title), do something like this:
$last_category = "";
while(/* get a row here */) {
if( $last_category != $row['category']) {
if( $last_category != "") echo "</ul>";
echo "<ul>";
$last_category = $row['category'];
}
echo "<li>".$row['title']."<li>";
}
if( $last_category != "") echo "</ul>";

Answer 4

SELECT * FROM products ORDER BY category. This is to sort using category, your example output file seems different what are you trying to do?