<?php

$connection= mysqli_connect("localhost","root","","invoices");

$invID = $_POST['ID'];

 $query= "SELECT a.in_no, a.client, a.add, a.Date, a.subTotal a.gTotal, b.id, b.item, b.strength, b.quantity, b.price from invoice a, invoiceItems b where a.in_no = b.in_id AND  in_no = '$invID' ";

 $runQuery = $connection->query($query);

 if($runQuery->num_rows > 0) {
 $result = $runQuery->fetch_array();
 } // if num_rows

 $connection->close();
 echo json_encode($result);
?>

function Invoice (ID = null) {

if(ID) {
$.ajax({
    url: 'fetch.php',
    type: 'post',
    data: {ID: ID},
    dataType: 'json',
    success:function(response) {

        // invoice id
        $(".footerClass").append('<input type="hidden" name="Id"
        id="invoiceiD" value="'+response.in_no+'" />');

        // invoice no
        $("#No").val(response.in_no);
        // Name
        $("#Name").val(response.client);
        // pat.Address
        $("#Add").val(response.add);
        // invoice date
        $("#Date").val(response.Date);

        //this data should be in loop
        $('#item_').val(response.item);
        $('#quantity').val(response.quantity);
        $('#price').val(response.price);
        $('#total').val(response.quantity*response.price);
        calculateTotal();
        }
     });
    }else {
        alert('error loading data');
    }
 }