使用mysqli SELECT查询的预备语句不起作用

Question

我正在学习使用预准备语句从db获取内容。这是我拼凑在一起的代码，但它没有返回任何内容。

$question_id = strip_tags(mysqli_real_escape_string($conn, $_GET['id']));    
$sql = "
    SELECT
        *
    FROM
        question_index
    WHERE
        id = ? AND
        remove = '0' AND
        active = '1' AND
        publish_date <= '$current_time'
    LIMIT
        1
";

$stmt = $conn->prepare($sql);
$stmt->bind_param('i', $question_id);
$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    // Localize 
    foreach($row as $key=>$value) { 
        ${$key} = $value;
    }

    // Current Question
    $current_question = $question;

    // Publish Date
    $current_publish_date = date('F d, Y g:i A', strtotime($publish_date));
}