comment-reply jquery获取回复并将其存储在表中但不存储于comment_id

I have created a comment-reply system usign php and jquery. My code includes a function for comments and then using jquery I am trying to get comments_id which is the id for each comment and the reply and save it a table called comments_reply. My only problem is that I cannot get comments_id, but I can successfuly get reply and store it in the comments_reply table. Any idea why my code cannot get comments_id to store it?

This is my function in php including jquery:

<?php

<script>

$(document).ready(function(){   
$('.reply').keyup(function(e){
    if(e.keyCode == 13){
        var comments_id = $(this).attr('comments_id');
        var reply = $(this).val();
        $.post('reply.php', {comments_id:comments_id, reply:reply});  
        $('.reply').val('');    
    }

});

});

</script>


function getComments(){

$comments = "";

$sql = mysql_query("SELECT * FROM comments ORDER BY comment_date DESC ") or die (mysql_error());

if(mysql_num_rows($sql) == 0){
    $comments = " <div class='each_comment'> There are no comments ...</div> ";
}
else
{
  while ($row= mysql_fetch_assoc($sql)){        

$comments .= "User Says : <div class='each_comment'> ".$row['comment_date']."".$row['comment']."

<input type='text' class='reply' comments_id='<?php ".$row['comments_id']." ?>' />

    </div> "; 
  }
 }
   return $comments;  
}
?>

And this is my page: reply.php

<?php

$comments_id = $_POST['comments_id'];

$reply = $_POST['reply'];


mysql_query("INSERT INTO comments_reply VALUES ('', '$comments_id', '$reply') "); 

?>

to prevent any confusion between your value and propery name (being exactly the same) when submitting to the server you should add quotes to the name.

$('.reply').keyup(function(e){
    if(e.keyCode == 13){
        var comments_id = $(this).attr('comments_id');
        var reply = $(this).val();
        $.post('reply.php', {"comments_id":comments_id, "reply":reply});  
        $('.reply').val('');    
    }

});

that may even fix your issue

EDIT

I would also change your custom html attribute names like so:

change comments_id to data-comment-id and reply to data-reply for the sake of convention and possibly usefull html5 support and don't forget to update all usages (in html and javscript code).

I have also noticed your sql code VALUES ('', '$comments_id', '$reply') shows that you are inserting a blank value to the first column in the table is there a reason for this?

EDIT2

For when people look at what the answer was instead of reading the comments of this answer I will put it here:

replace

<input type='text' class='reply' comments_id='<?php ".$row['comments_id']." ?>' />

with

<input type='text' class='reply' comments_id='{$row['comments_id']}' /> 

or the id will include unwanted characters.