如何使用AJAX刷新div？

Question

I know there are many entries about this topic but I dont get my code to work. I build a div container (this is the div I want to refresh every second) which includes 3 other div containers.

My code so far: index.php

<div id="ajax">
   <div class="row d-flex align-items-center">
      <div class="showPGF"> 
         <?php
            $controller->getEntries();
         ?>
      </div>
   </div>

   <div class="row d-flex align-items-center">
      <div class="showNGi_sample"> 
         <?php
            $controller->getUsers();
         ?>
      </div>
   </div>

   <br>

   <div class="row d-flex align-items-center">
      <div class="showNGi_sample"> 
         <?php
            $controller->getPGFEntries();
         ?>
      </div>
   </div>
</div>

script.js

$(document).ready(function () {

function ajax(){
        $('#ajax').load('index.php',function() {
            $(this).unwrap();
        });
    }

    ajax(); // This will run on page load
    setInterval(function(){
        ajax() // this will run after every 1 seconds
    }, 1000);

}

I want to get the DIV with the "ajax" id to get reload every second. Because I want to get always the current Entries/Users from my database (execute the php call every second). But currently it dont refresh and I need to press F5 to get the new entries shown.