登录Facebook，获取数据，如果数据不存在，则存储在MySQL数据库中

我用javascript sdk做了一个Facebook登录。我可以得到姓名、身份证和照片，但不能得到电子邮件。我发送的名称与ajax php，所以它可以在数据库中插入，但它插入空字段。所以我的问题是如何将姓名插入数据库以及如何获取电子邮件。

// This is called with the results from from FB.getLoginStatus().
function statusChangeCallback(response) {
    console.log('statusChangeCallback');
    console.log(response);
    // The response object is returned with a status field that lets the
    // app know the current login status of the person.
    // Full docs on the response object can be found in the documentation
    // for FB.getLoginStatus().
    if (response.status === 'connected') {
        // Logged into your app and Facebook.
        testAPI();
    } else if (response.status === 'not_authorized') {
        // The person is logged into Facebook, but not your app.
        document.getElementById('status').innerHTML = 'Please log ' +
                'into this app.';
    } else {
        // The person is not logged into Facebook, so we're not sure if
        // they are logged into this app or not.
        document.getElementById('status').innerHTML = 'Please log ' +
                'into Facebook.';
    }
}
// This function is called when someone finishes with the Login
// Button.  See the onlogin handler attached to it in the sample
// code below.
function checkLoginState() {
    FB.getLoginStatus(function (response) {
        statusChangeCallback(response);
    });
}
window.fbAsyncInit = function () {
    FB.init({
        appId: 'XXX',
        cookie: true, // enable cookies to allow the server to access 
        // the session
        xfbml: true, // parse social plugins on this page
        version: 'v2.2' // use version 2.2
    });
    // Now that we've initialized the JavaScript SDK, we call 
    // FB.getLoginStatus().  This function gets the state of the
    // person visiting this page and can return one of three states to
    // the callback you provide.  They can be:
    //
    // 1. Logged into your app ('connected')
    // 2. Logged into Facebook, but not your app ('not_authorized')
    // 3. Not logged into Facebook and can't tell if they are logged into
    //    your app or not.
    //
    // These three cases are handled in the callback function.
    FB.getLoginStatus(function (response) {
        statusChangeCallback(response);
    });
};
// Load the SDK asynchronously
(function (d, s, id) {
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id))
        return;
    js = d.createElement(s);
    js.id = id;
    js.src = "//connect.facebook.net/en_US/sdk.js";
    fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
// Here we run a very simple test of the Graph API after login is
// successful.  See statusChangeCallback() for when this call is made.
function testAPI() {
    console.log('Welcome!  Fetching your information.... ');
    FB.api('/me', function (response) {
        console.log(JSON.stringify(response));
        console.log('Successful login for: ' + response.name);
        document.getElementById('status').innerHTML =
                'Thanks for logging in, ' + response.name + '!';
    });
}
function Login()
{
    FB.login(function(response) {
       if (response.authResponse) 
       {
            getUserInfo();
        } else 
        {
         console.log('User cancelled login or did not fully authorize.');
        }
     },{scope: 'email,user_photos,user_videos'});
}
function Logout()
{
    FB.logout(function(){document.location.reload();});
}
function getPhoto()
{
    FB.api('/me/picture?type=normal', function(response) {
        var str="<br/><b>Pic</b> : <img src='"+response.data.url+"'/>";
        document.getElementById("status").innerHTML+=str;
    });
}
function getUserInfo() {
    FB.api('/me', function(response) {
        var str="<b>Name</b> : "+response.name+"<br>";
            str +="<b>Link: </b>"+response.link+"<br>";
            str +="<b>Username:</b> "+response.username+"<br>";
            str +="<b>id: </b>"+response.id+"<br>";
            str +="<b>Email:</b> "+response.email+"<br>";
            str +="<input type='button' value='Get Photo' onclick='getPhoto();'/>";
            str +="<input type='button' value='Logout' onclick='Logout();'/>";
        document.getElementById("status").innerHTML=str;
        var username_fb = 'response.name=' +response.name;
        $.ajax({
            url: "check_user_fb.php", //This is the page where you will handle your SQL insert
            type: "get",
            data: "username_fb=" + username_fb, //The data your sending to some-page.php
            success: function(){
                console.log("AJAX request was successfull");
            },
            error:function(){
                console.log("AJAX request was a failure");
            }
        });
    });
}
<div scope="public_profile,email" onclick="Login();">
    Login
</div>

if ($_SERVER['REQUEST_METHOD'] == 'GET') {
    global $return;
    if (insertIntoDatabase()) {
        //return "Data inserted successfully!";
        echo json_encode($return);
    } else {
        echo json_encode($return);
    }
}
function insertIntoDatabase() {
    // Function that inserts username, password and email defined by user into database
    global $return;
    //Connect to a database
    include 'includes/database.php';
    // Sanitize inputs
    $username = $_POST['username_fb'];
    //Insert fields into database
    $sql = "INSERT INTO users (username) VALUES ('$username')";
    (mysqli_query($link, $sql));
    // close connection
    mysqli_close($link);
}