Jquery - parsererror - Unexpected end of JSON input - php

Question

I'm trying to retrieve info from my database and display the information in a table generated by JQuery. I had done this before, and with using the exact same code it doesn't work anymore. I've looked up several other questions about this, but none of them has given me an answer.
This is the situation: An user select a value from the select menu, by selecting a value, that value gets sent and used to retrieve the right key for the right data. Then, by pressing a button the data should appear in a table. In order to accomplish this, I am using 3 ajax calls, one for populating the select box, one to send the right value, and another one to retrieve the needed data. The first two work perfectly, but not the last one.
My browser receives the data (see below) but the table does not appear and I'm getting a 'Unexpected end of JSON input' error. Can anyone help me out with this?
HTML/Jquery of the Ajax with the error:
function BekijkGegevens() {
$.ajax({
type: 'GET'
, data: {}
, dataType: 'json'
, url: "https://projectmi3.000webhostapp.com/webservices/bekijk.php"
, success: function (rows) {
$('#output').append("<table><tr><th> datum</th><th>stand</th></tr>")
for (var i in rows) {
var row = rows[i];
var datum = row[1];
var stand = row[0];
$('#output').append("<tr><td>" + datum + "</td><td>" + stand + "</td></tr>");
}
$('#output').append("</table>");
}
, error: function (JQXHR, TextStatus, ErrorThrow) {
console.log(JQXHR);
console.log(TextStatus);
console.log(ErrorThrow);
}
})
}
PHP:
<?php
include_once('confi.php');
error_reporting(E_ALL);
if (isset($_POST['teller']))
{
$teller = mysqli_real_escape_string($conn,$_POST['teller']);
$sql2="SELECT sta_stand,sta_datum FROM stand WHERE teller_id = '$teller'";
$result = $conn -> query($sql2);
//$query2 = mysql_query($sql2) or trigger_error(mysql_error()." ".$sql2);
$data2=array();
while ($row = mysqli_fetch_row($result))
{
$data2[]=$row;
}
echo "{data:" .json_encode($data2). "}" ;
}
?>
Thanks for any help that you can provide.
EDIT: Forgot to put my browser network, here it is.
http://puu.sh/uzI4f/a9ed1e0be5.png
EDIT2: I've split the PHP script into two seperate files, and tries to use a session variable to pass the needed key as suggested in the comments. Yet I am still getting the same error. Hereby the two new PHP files:
This one is used to send the key from Jquery to PHP:
<?php
include_once('confi.php');
error_reporting(E_ALL);
session_start();
if (isset($_POST['teller']))
{
$teller = mysqli_real_escape_string($conn,$_POST['teller']);
$_SESSION['teller'] = $teller;
}
?>
This one is used to get the needed information:
<?php
include_once('confi.php');
error_reporting(E_ALL);
session_start();
if (isset($_SESSION['teller']))
{
$sql2='SELECT sta_stand,sta_datum FROM stand WHERE teller_id ="' .$_SESSION['teller'].'"' ;
$result = $conn -> query($sql2);
//$query2 = mysql_query($sql2) or trigger_error(mysql_error()." ".$sql2);
$data2=array();
while ($row = $result-> fetch_row())
{
$data2[]=$row;
}
echo json_encode($data2);
}
?>

Answer 1

First, some warnings (in accordance with this link):
Little Bobby says your script is at risk for SQL Injection Attacks. Learn about prepared statements for MySQLi. Even escaping the string is not safe! Don't believe it?
You should test against the session variable in your second script, which should look like this:
<?php
include_once('confi.php');
error_reporting(E_ALL);
session_start();
if (isset($_SESSION['teller']))
{
$teller = $_SESSION['teller'];
$sql2="SELECT sta_stand,sta_datum FROM stand WHERE teller_id = '$teller'";
$result = $conn -> query($sql2);
$data2=array();
while ($row = mysqli_fetch_row($result))
{
$data2[]=$row;
}
echo json_encode(['data'=> $data2]);
}
?>
Please note that I am also appending the 'data' properly to the JSON instead of just trying to "glue" (as said by Denis Matafonov) the JSON string together.

Answer 2

Dont try to glue data to string, like this:
echo "{data:" .json_encode($data2). "}" ;
Use simple
echo json_encode(['data'=> $data2]);
It should produce the same result if everything goes right, but wouldnt break up json if your $data2 is null
Declare your $data2 in the begginng, before if statement:
$data2 = [];
if (isset($_POST['teller'])) {
//do stuff and redefine $data2 or fill it;
}
//always echo valid json, event if no $POST["teller"] has arrived
echo json_encode(['data' => $data2]);