No Access-Control-Allow-Origin header is present on the requested resource. Origin 'null' is therefore not allowed access. - Phonegap [duplicate]

I have read about this method json and I just do not understand and do not know what to fix, I'm using another domain to get json.

Here is my code:

$(function(){
    var url = "http://website.com/json.php";
    $.getJSON(url, function(result) {
        console.log(result);
        $.each(result, function(i, field) {
            var id = field.id;
            var title = field.title;
            $(".class").append("<a href='page.html?id=" + id + "&title=" + title +");
        });
    });
});

Error:

  

XMLHttpRequest can not load link . In 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.

How can I pass this to another code, like this:

 $.ajax({
        url: url,
        crossDomain: true,
        data: form,
        dataType: 'json',
        success: function(data) {
            console.log(data);
        },
        type: 'POST'
    });

Json.php:

<?php
    header("Access-Control-Allow-Origin: *");
    include "db.php";
    $data=array();
    $q=mysqli_query($con,"select * from 'course_details'");
    while ($row=mysqli_fetch_object($q)){
        $data[]=$row;
    }
echo json_encode($data);
?>

Db.php

<?php
    header("Access-Control-Allow-Origin: *");
    $con = mysqli_connect("localhost","user","pass","db") or die ("could not connect database");
?>

I'm opening the index.html by the same chrome, not by localhost, and I'm making the call in another domain (website.com/json.php), and have this problem.

Some people put it as a duplicate, but it is not duplicated, I would like a solution that the other does not have, I need a clear answer.