Format for Sending Data in PHP and retrieve it (especially for multiple queries)

I have a php here

<?php
    /* Initiate Connection */
    require 'conn.php';

    /* Filter Criteria */
    $startdate    = $_POST['startdate'];
    $enddate      = $_POST['enddate'];
    $fsp          = $_POST['fsp'];

    /* Queries */
    $query    = 'MYSQL Query Here';

    /* Generate Whole Sales Report */
    $rs    = mysqli_query($con,$query);

    /* Sales Summary */
    while ($array_data = mysqli_fetch_row($rs)) {
        $data[] =  $array_data; 
    }

    /* Output */
    echo json_encode($data);
?>

This php code outputs a data from mysql in a form of rows and columns. my question is this but before that here is my code when passing the data in a php file.

$(document).ready(function() {
    $('#btngenerate').click(function(e) {
        $.ajax({
            url: 'gen_report.php',
            type: "POST",
            datatype: 'json',
            data: {
                    startdate: 'Data',
                    enddate:   'Data',
                    fsp:       'Data'
            },
            success: 
                function(data) {
        });     
    });
});

My question here is can someone lead me in the right path? My target here is to create a format or set of codes using this codes that I can recycle. I mean use it anywhere like passing data to php retreive it and so on.

My target here is what If my myphp file is composed of multiple queries and json_encode which is where? I means json_encode1 = html_table1,json_encode2 = html_table2 and so on how can I achieve it?

TYSM