I always get Warning: mysqli_fetch_row() expects parameter 1 to be mysqli_result, boolean given [duplicate]

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• mysqli_fetch_array()/mysqli_fetch_assoc()/mysqli_fetch_row() expects parameter 1 to be resource or mysqli_result, boolean given 33 answers

$query = "SELECT question, id FROM qs ORDER BY id DESC";
$results = mysqli_query($db, $query);

while ($row = mysqli_fetch_row($results)) {
    echo "<div class='question'>".$row[0]." / ".$row[1]."</div><form method='POST' action='index.php'><input type='text' name='answer-box' placeholder='Answers'><input name='replyb' value='Reply' type='submit'></form><br><br>";
}
?>
$answer = @$_POST['answer-box'];
$button = @$_POST['replyb'];

if (isset($button)) {
    $sql_answer = "INSERT INTO `answers` (`answer`,`id`) VALUES ('$answer', '$row[1]')";
    $result_answer = mysqli_query($db, $sql_answer);
    $row_answer = mysqli_fetch_row($result_answer);
} else {

}

?>