Please how can i retrieve join query data from mysql in flutter?

I have the following code that logs a user in if successfully authenticated and it will pass a username to the dashboard page. How can I use the transferred username to get only the details of the specific user in mysql and display it in the Dashboard screen?………………………………

`Future login() async {
    var url = 'https://xxxxxxxxxxxxxx.com/login.php';
    var response = await http.post(Uri.parse(url), body: {
      "svcNo": user.text,
      "password": pass.text,
    });
    var data = json.decode(response.body);
    if (data.toString() == "Success") {
      Fluttertoast.showToast(
        msg: 'Login Successful',
        backgroundColor: Colors.green,
        textColor: Colors.white,
        toastLength: Toast.LENGTH_SHORT,
      );
      // ignore: use_build_context_synchronously
      Navigator.push(
        context,
        MaterialPageRoute(
          builder: (context) => DashBoard(
            svcnoIPPIS: user.text,
          ),
        ),
      );
    } else {
      Fluttertoast.showToast(
        backgroundColor: Colors.red,
        textColor: Colors.white,
        msg: 'Svc No and password invalid',
        toastLength: Toast.LENGTH_SHORT,
      );
    }
  }
Future<Object> getData() async {
    var url = 'https://xxxxxxxxxxxxxxxxx.com/getData.php/';
    var response = await http.post(Uri.parse(url), body: {
      "svcNo": widget.svcnoIPPIS,
    });
    final items = json.decode(response.body).cast<Map<String, dynamic>>();
    List<Object> user = items.map<User>((json) {
      return User.fromJson(json);
    }).toList();
    return user;
    if (response.statusCode == 200) {
      return User.fromJson(jsonDecode(response.body));
    } else {
      throw Exception('Failed to load album');
    }
    }
<?php
    $db = mysqli_connect('localhost','$username','$password','$theDatabase');
    $svc_no = $_POST['svcNo'];
    $sql = "SELECT name, rank, start_date, SUM(amount) from $table u join $anotherTable c on u.svcNo_IPPIS = c.svcNo_IPPIS WHERE c.svcNo_IPPIS = '.svc_no.'";
    $result = mysqli_query($db,$sql);
    $finalResult=array();
     while($fetchData=$result->fetch_assoc()){
    $finalResult[]=$fetchData;
    }
    echo json_encode($finalResult);
    ?>`