Getting Data from SQL Database

[ritu9901]

Hi all,
A month back, I worked on an experiment where a set of participants completed a multi-attribute-choice project. On each trial, participants saw two options and chose which one they would prefer. In the next part of my experiment, I want to present each of the previous participants' choices to a new participant. In order to achieve that, I want to save the new participants' data to a database and retrieve their row numbers. Row number would further match my previous database.

I am able to save the database. I am stuck at getting row number as variable in my jsPsych script.
Here is what I am thinking of doing:

Add get_data function to utilities.js:

function get_data(){
var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    var response =xmlhttp.responseText;
    }
  }
xmlhttp.open("GET","getData.php",true);
xmlhttp.send();
}

This is my getData.php:

<?php

include('database_config.php');

$subject_info = json_decode(file_get_contents('php://input'), true);

try {
  $conn = new PDO("mysql:host=$servername;port=$port;dbname=$dbname", $username, $password);

  $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

  $stmt = $conn->prepare("SELECT ROW_NUMBER() OVER() FROM `$table_name` WHERE `$subject_id` = "subject_name");");

  $stmt->execute();
$conn = null;

?>

Clearly, this isn't working. Can anyone help with this or suggest any other approach, please? Thank you.!