Ajax, PHP, MySQL returning sql table - php

Question

I have the following Ajax code to send information from an HTML form to a PHP file.
$(document).ready(function(){
$('#txt').load( '../../do_comment.php' );
});
$(function(){
$("#submit").click(function(e) {
e.preventDefault();
var name = $("#user_name").val();
var comment = $("#user_comment").val();
var ID = '2'; //must change for each post
$.ajax({
type: "POST",
url: "../../do_comment.php",
data: {user_name:name, user_comment:comment, ID:ID},
success: function(){
$('#txt').load( '../../do_comment.php' );
},
error:function(e){alert("it failed");}
});
});
});
In my PHP file I declare the variables like this:
$name = $_POST[user_name];
$comment = $_POST[user_comment];
$ID = $_POST[ID];
And correctly populate my database with this:
if($_POST[user_comment] != Null) {
$sql = "INSERT INTO $table_name (post_ID, user_name, comments)
VALUES ('$ID','$name', '$comment')";
$result = #mysql_query($sql,$connection) or die(mysql_error());
}
The problem is none of the variables will echo any sort of value, and when I try to query the database it only works if I hard code the ID value in instead of using the variable.
$data = mysql_query("SELECT * FROM $table_name WHERE post_ID =
'".mysql_real_escape_string($ID)."'") or
die(mysql_error());

Answer 1

Use the following when gathering from $_GET/$_POST/$_REQUEST:
$name = $_POST['user_name'];
$comment = $_POST['user_comment'];
$ID = $_POST['ID'];
Notice the tics. Proper syntax is $_POST[''].
Have you checked the database to make sure the proper values are being inserted?
Also, if the post_id is an integer, don't use tics
SELECT * FROM table WHERE post_ID = 1234
NOTICE: do not use MySQL_*, it has been deprecated in PHP 5.5. Use MySQLi or PDO. Watch out for SQL injections as well, especially when using MySQL_*.