check if user exists with php and mysql stmt - php

Question

I'm creating an authentification file with php and mysql, but I have this mistake in this line:
$stmt2->bind_param('ss',$twitter_id, $name);
The error message is
Call to a member function bind_param() on a non-object in ...
Where's my mistake?
$name in my database is a VARCHAR
$twitter_id in my database is a VARCHAR
$bd is my database connection
If a user is already registered, it should show me a message saying "User already registered", and if the user isn't registered, it should insert a new id and name in my database.
session_start();
if (!isset($_SESSION['userdata'])) {
header("location: index.php");
} else {
$userdata = $_SESSION['userdata'];
$name = $userdata->name;
$twitter_id = $userdata->id;
$stmt = $bd->prepare("SELECT ID_TWITTER FROM USERS");
$stmt->execute();
$stmt->bind_result($checkUser);
if ($stmt->fetch()) {
if($checkUser!==$twitter_id){
$cSQL = "INSERT INTO USERS (ID_TWITTER, FULL_NAME) VALUES(?,?)";
$stmt2 = $bd->prepare($cSQL);
$stmt2->bind_param('ss',$twitter_id, $name);
$stmt2->execute();
$stmt2->close();
} else {
echo "User already exits";
}
}
$stmt->close();
}

Answer 1

Could it be a typo? does $bd exist or should it be $db ?

Answer 2

Shameless plug: I do this exact thing in a project I have on github. Feel free to use the classes for whatever you like; they are mostly copy-pastable.
Your real issue is that $bd->prepare() returned false.
Check that you actually called it correctly and set it to new mysqli(*params)
The error Call to a member function ... on a non-object in ... means that $db is not an object, which means that it was not instantiated to an object. Thus, $this->method() isn't possible. bind_param(string $format, mixed &*vars); uses pass-by-reference and if this fails, it throws an error.
Try it yourself by sticking this in there:
$stmt->bind_param("ss", "string", "string");
To get around this issue where it can fail, check if $db->prepare() returns true:
if ($query = $bd->prepare($sql)) {
//stuff
}
In addition, in the first query you do it is probably not a good idea to be adding the overhead of a prepare for a single query that only checks row count without user input.

Answer 3

Solved : it works now
$stmt = $bd->prepare("SELECT ID_PROVIDER FROM USERS WHERE ID_PROVIDER = ?");
$stmt->bind_param('s', $twitter_id);
$stmt->execute();
$stmt->bind_result($checkUser);
while ($stmt->fetch()) {
$result = $checkUser;
}
if (empty($result)) {
$cSQL = "INSERT INTO USERS (ID_TWITTER, FULL_NAME)
VALUES(?,?)";
$stmt2 = $bd->prepare($cSQL);
$stmt2->bind_param('ss', $twitter_id, $name);
$stmt2->execute();
$stmt2->close();
}else {
echo "User already exits";
}