How to retrieve specific data from the database using ajax

this is my ajax code to retrieve all data from a php file:

<script type="text/javascript">
 $(document).ready(function() {
    $("#display").click(function() {
      $.ajax({    //create an ajax request to load_page.php
        type: "GET",
        url: "read.php",
        dataType: "html",   //expect html to be returned
        success: function(response){
<h3 align="center">Manage Student Details</h3>
<table border="1" align="center">
       <td> <input type="button" id="display" value="Display All Data" /> </td>
<div id="responsecontainer" align="center"></div>

And this is part of my php file witch retrieves data from database and stores it into variables :

  while($row = mysqli_fetch_assoc($result)){
    $user_id = $row["user_id"]
    $user_name = $row["user_name"]
    $user_text = $row["user_text"]

If I echo the above variables then they will be shown in my html page whitch contains ajax codes but I want to get each variable with ajax and do some operations on them and then show them in my html page
There is Simple html dom in php to get one page's html elements is there anything like php simple html dom for ajax? if not then how is it possible to do the things I said?
I'll be appreciate that if someone can help me with this:)

Server side

$array = array();
while($row = sqlsrv_fetch_array( $stmt, SQLSRV_FETCH_ASSOC)){

                        array_push(//what you need);

echo json_encode($array);

And on the client side

success: function(response){
            data = $.parseJSON(JSON.stringify(returnedData)); 


Note that JSON.stringify is not needed however I like it data is now an object and you can access its properties with data.propertyname