The way I would approach this is to use a client side AJAX request to a php fetch script that looks at the logged in users SESSION['id'] to find all comments made by post authors that are children of a comment the logged in user has made

Frontend

You may use whatever way you want to send a request to your PHP script, I have used jQuery for simplicity.

The jQuery $.ajax function will be ran on the page continuously to check for notifications. This has been done by enclosing it in a setInterval function.

This code is not tested so not 100% sure on the namespacing of the PHP array you will get back. Best to console.log the data object in the success handler here.

您会注意到，这里有对readComment.php脚本的引用，这可以是一个简单的脚本，用于设置comments.status = 1指示读取状态。

  setInterval(function() {
    $.ajax({
   url:"fetch.php",
   method:"GET",
   success:function(data)
   {
    console.log(data)
    data.forEach(function(i,v) {
        $( "#notifications" ).append( "<a href=readComment.php?id=" + v.id + ">unread notification</p>" );
    });

   }
  });
 }
}, 60 * 1000); // This will run every minute to check for notifications

服务器

fetch.php

我在这里使用带有两个WHERE IN子句的select语句来检索帖子作者发表的所有评论，这些评论是已登录用户发表的评论的子级。我没有对此测试进行100％的测试，因为我尚未测试过，但这应该可以帮助您入门。

$query = "SELECT 
    *
FROM
    comments
WHERE
    comments.user_id IN (SELECT posts.post_user FROM posts)
AND
    comments.parent_comment_id IN (SELECT comments.id FROM comments WHERE comments.user_id = ".SESSION['id'].")"
AND 
    comments.status = 0";

$result = mysqli_query($connection, $query);

header("Status: 200");
header('Content-Type: application/json');
echo json_encode(array('data' => mysqli_fetch_array($result) )); 
die;

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