How to call function in file2.php with parameters from file1.php for JSON

[Gennadiy81]

Hi everyone, I have some questions, help me advice.
in the FILE1.php with java scrip I put up some php code in a head of file.
my task is that the user would have seen a drop-down box, choose the item he wants and clicks on it, but all the processing took place in the FILE2.php

How can I send a value from FILE1.php  to the FILE2.php ? but it must be while AJAX call this FILE2.php  in other case it will be without my parameters from FILE1.php ?
It must be somethind like that
function drawBasic(){   

              var jsonData = $.ajax({
              url: "FILE2.php:getDataString($var1, $var2...etc)", // Function from FILE2.php
              dataType: "json",
              async: false
              }).responseText;   
---------------------------------------------------------------------------------
FILE1.PHP
<?php
//SQL Query for Dropdown-List in the same page
//FORM must be send via $_SERVER["PHP_SELF"]


FILE1.PHP
?>

    <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
    <script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
    <script type="text/javascript">


function drawBasic(){   

              var jsonData = $.ajax({
              url: "FILE2.php",
              dataType: "json",
              async: false
              }).responseText;   


            var data = new google.visualization.DataTable(jsonData);
            var options = {
                hAxis: {
                  title: 'Weeks'
                },
                vAxis: {
                  title: 'Value'
                },
            };

    var chart1 = new google.visualization.LineChart(document.getElementById('chart_div'));

     
    chart1.draw(data, options);

 
    }

google.charts.load('current', {packages: ['corechart', 'line']});
google.charts.setOnLoadCallback(drawBasic);
    </script>
   
<table border="0" align="center">
    <tr>
        <td>   <div id="chart_div" style="width: 850px; height: 500px;"></div> </td>   
    </tr>   
</table>




---------------------------------------------------------------------------------------------------------------------

FILE2.PHP
<?php


     

$db = mysqli_connect("localhost","root","p@$WorDt","db");
function getDataString($manager_group){
    global $db;
    $i = 0;

    $query="select date, sum(salary) as sum_gr from manager where manager_group=$manager_group";

   
    $res = mysqli_query($db,$query);
    $data = '{"cols": [';
    $data .= '{"id":"","label":"DATUM","type":"number"},';
//    $data .= '{"id":"","label":"SALARY","type":"number"}';
    $data .= '{"id":"","label":"'GROUP'","type":"string"}';

    $data .= '],"rows": [';

    while($row = mysqli_fetch_assoc($res)){
       

        $data .='{"c":[
                             {"v":"'.$row[date].'","f":null},
                             {"v":"'.$row['sum_gr'].'","f":null}

]},';
       
    }
    $data=rtrim($data,',');
    $data .=']}';
    return $data;
}
echo getDataString();


?>