extracting info from database to html page error - php

Question

i'm very new to PHP so i apologize if this is a simple fix but i'm experiencing a weird issue. I've created a website that uses facebook authentication. once they login, their information gets stored in a database I've created. i then created some functions that display the users facebook image and name on the profile page of my website. problem is sometimes it shows, and other times i receive this error. "notice: undefined index: fbid in /PATH/ on line 132". Here is the code.
<div id="userInfo" class="userInfo">
<h1> <?php
$dbHost = "localhost";
$dbUsername = "root";
$dbPassword = "root";
$dbName = "facebooklogin";
$conn = new mysqli($dbHost, $dbUsername, $dbPassword, $dbName);
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT first_name, last_name, picture FROM users WHERE
oauth_uid = '".$_SESSION['fbid']."'";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
echo " ". $row["first_name"]." ". $row["last_name"]."";
}
} else {
echo "0 results";
}
$conn->close();
?></h1>
userData.php
<?php
session_start();
include 'dbConfig.php';
$userData = json_decode($_POST['userData']);
if(!empty($userData)){
$oauth_provider = $_POST['oauth_provider'];
$_SESSION['fbid'] = $userData->id;
var_dump($_SESSION);
$prevQuery = "SELECT * FROM users WHERE oauth_provider =
'".$oauth_provider."' AND oauth_uid = '".$userData->id."'";
$prevResult = $db->query($prevQuery);
if($prevResult->num_rows > 0){
$query = "UPDATE users SET first_name = '".$userData-
>first_name."', last_name = '".$userData->last_name."', email =
'".$userData->email."', gender = '".$userData->gender."', locale =
'".$userData->locale."', picture = '".$userData->picture->data->url."',
link = '".$userData->link."', modified = '".date("Y-m-d H:i:s")."'
WHERE oauth_provider = '".$oauth_provider."' AND oauth_uid =
'".$userData->id."'";
$update = $db->query($query);
}else{
$query = "INSERT INTO users SET oauth_provider =
'".$oauth_provider."', oauth_uid = '".$userData->id."', first_name =
'".$userData->first_name."', last_name = '".$userData->last_name."',
email = '".$userData->email."', gender = '".$userData->gender."',
locale = '".$userData->locale."', picture = '".$userData->picture-
>data->url."', link = '".$userData->link."', created = '".date("Y-m-d
H:i:s")."', modified = '".date("Y-m-d H:i:s")."'";
$insert = $db->query($query);
}
}
?>

Answer 1

It seems that you don't have the variable set when you use it in the query.
Check it before the query, like:
if (isset($_SESSION['fbid'])) {
$sql = "SELECT first_name, last_name, picture FROM users WHERE
oauth_uid = '".$_SESSION['fbid']."'";
$result = $conn->query($sql); } else {
// not logged in
}
To check the values of $_SESSION, just do a var_dump($_SESSION) and you can see what is set.