Getting data from firebase web

I am trying to fetch the data for a website using javascript. The problem I am getting is that I am unable to get the key of Users-->Rider-->rating-->key-->("Rating Value"). I am unable to find a syntax of it.

I want to retrieve the value of rating within this jQuery.

>

 <script>

database = firebase.database();

var ref = firebase.database().ref().child("Users").child("Riders");

ref.on('value',gotDataa,errDataa);

function gotDataa(data){
    //console.log(data.val());
    var Riders = data.val();
    var keys=Object.keys(Riders);
    console.log(keys);
    for(var i=0 ; i<keys.length;i++)
    {
        var k=keys[i];
        var car = Riders[k].car;
        var cnic = Riders[k].cnic;
        var email = Riders[k].email;
        var name = Riders[k].name;
        var phone = Riders[k].phone;
        var service = Riders[k].service;
        var rating = data.child("rating").child(keys).val();


$("#table_body").append("<tr><td>" + name + "</td><td>" + phone +"</td><td>"+ email+"</td><td>"+ cnic +"</td><td>"+car+"</td><td>"+service+"</td><td>"+rating+"</td></tr>");

    }
}

function errDataa(err){

    console.log('Error');
    console.log(err);

}
</script>

I am getting null value of rating please correct me where I am wrong.