我有一个页面显示存储在mysql数据库中的文章。当文章被创建时，用户可以选择他们想让文章在多长时间内可见，我正在试图找出如何在确定的时间内只显示文章。下面是我的一些代码（希望能显示我正在尝试的逻辑）。

//Query database

$sql = <<<SQL
    SELECT *
    FROM `posts`
SQL;

if(!$result = $db_connection->query($sql)){
    die('There was an error running the query [' . $db_connection->error . ']');
}

while($row = $result->fetch_assoc()){

    //The date the post was made
    $date_of_post = $row['date_of_post'];
    //The duration of the post in days eg 7.
    $duration = $row['duration'];
   //Attempting to add duration to date
    $newdate = strtotime($duration, $date_of_post);
    //Only show posts that are still valid, eg date + duration is less than today's date
    if($newdate > now()){
        echo '<h2>Post Title</h2>';
        echo '<p>Date of Posted:'.$date.'</p>';
    }
}