Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\

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PHP

I'm trying to check my data before inserting it into the database, but this error always appear

What I have tried:

<pre>if(isset($_POST['submit'])){
    

$first_name = test_input($_POST["firstname"]);
$last_name = test_input($_POST["lastname"]);
$id = test_input($_POST["member_id"]);
$username = test_input($_POST["username"]);
$password = test_input($_POST["password"]);
$email = test_input($_POST["email"]);
$membertype = test_input($_POST["membertype"]);
$phone = test_input($_POST["phonenumber"]);
$department = test_input($_POST["department"]);

 
  $query = "SELECT * FROM lms WHERE  ID='".$id."' OR email='".$email."' OR  user_name='".$username."' ";
$resultdata = mysqli_query($link , $query);
$data = mysqli_fetch_array($resultdata, MYSQLI_NUM);
    
if($data[0] > 1) {
    echo "User Already in Exists<br/>";
}

else
{
    $sql = "INSERT INTO `member` (`ID`, `first_name`, `last_name`, `member_type`, `password`, `email`, `phoneNo`, `department`, `user_name`)
VALUES ('$id', '$first_name', '$last_name','$membertype','$password','$email','$phone','$department','$username')";
    if (mysqli_query($link,$sql))
    {
        echo "You are now registered<br/>";
    }
    else
    {
 echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);    }
}
    
    
}
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}

?>

i have tried also this

$results = mysql_num_rows($resultdata);

and

$user = mysqli_fetch_assoc($resultdata);

but it gives me the same error, I know this error appears because of the query return false result, but I don't what else should I use