致命错误：未捕获错误：在布尔值|上调用成员函数fetch（） 仅限网络服务器

Question

The line saying <?php while ($row = $arne->fetch()) { ?> Seems to be working totally fine in localhost server with: Picture: localhost setup

<?php
    $arne = $db->query("SELECT *, AVG(correct_answers) AS average FROM result r, quiz q WHERE r.quiz_id=q.id GROUP BY quiz_id ORDER BY average");
    ?>
    <h1>Average Score</h1>
    <div id="table-wrapper">
        <div id="table-scroll">
            <table>
                <tr>
                    <th>Quiz</th>
                    <th>Result</th>
                    <th>Questions</th>
                </tr>
                <?php while ($row = $arne->fetch()) { ?>
                <tr>
                <td><a href="/quiz/<?=$row["quiz_id"]?>"><?=$row["name"]?></a></td>
                <td><?=floor($row["average"]*100 / $row["question_count"])?></td>
                <td><?=$row["question_count"]?></td>
                </tr>
                <?php } ?>
            </table>
        </div>
    </div>

But when using it on a webserver: Picture: webserver setup

I get the error:

Fatal error: Uncaught Error: Call to a member function fetch() on boolean in /var/www/html/php/pages/statistics.php:15 Stack trace: #0 /var/www/html/php/index.php(82): include() #1 {main} thrown in /var/www/html/php/pages/statistics.php on line 15

Line 15 is not line 15, but the line containing:

<?php while ($row = $arne->fetch()) { ?>

Thanks for help!