Example of sql injection in PDO

sql_injection.php

<?php

$dbh = new PDO('mysql:host=localhost;dbname=injection', 'root');

if(isset($_GET['id'])) {
    // Example of injectable sql query
    foreach($dbh->query('select * from users where id = ' . $_GET['id'] . ' LIMIT 1') as $query) {
        $user = $query;
    }
}

?>

<?php if(isset($user)): ?>
    <div>
        Found user
        <?= $user['name'] ?>
    </div>
<?php else: ?>
    <div>
        Search for a <a href="/?id=1">user</a>.
    </div>
<?php endif; ?>