web api php query not working

Question

So I have table RACUN and I want to select multiple rows where USERID = something

I have this query

<?php
class Racun{

    // database connection and table name
    private $conn;
    private $table_name = "RACUN";

    // object properties
    public $racunId;
    public $userId;
    public $broj;
    public $datum;
    public $vrednost;
    public $vrsta;

    // constructor with $db as database connection
    public function __construct($db){
        $this->conn = $db;
    }
    function read(){

        // select all query
        $query = "SELECT
                    RACUNID, USERID, BROJ, DATUM, VREDNOST, VRSTA
                FROM
                    " . $this->table_name . "
                WHERE
                    USERID = ?";

        // prepare query statement
        $stmt = $this->conn->prepare($query);

        $stmt->bindParam(1, $this->userId);

        // execute query
        $stmt->execute();

        return $stmt;
    }
}

It returns me that nothing has been found.

When I change $query to:

$query = "SELECT
    RACUNID, USERID, BROJ, DATUM, VREDNOST, VRSTA
FROM
    " . $this->table_name . "";

It returns me:

{"records":[{"racunId":"1","userId":"1","broj":"1200089","datum":"2018-03-09","vrednost":"127000","vrsta":"0"}]}

here is php file that runs read() function:

<?php
// required headers
header("Access-Control-Allow-Origin: *");
header("Content-Type: application/json; charset=UTF-8");

// include database and object files
include_once '../config/database.php';
include_once '../objects/Racun.php';

// instantiate database and product object
$database = new Database();
$db = $database->getConnection();

// initialize object
$racun = new Racun($db);

// query users
$stmt = $racun->read();
$num = $stmt->rowCount();

// check if more than 0 record found
if($num>0){

    // products array
    $racuns_arr=array();
    $racuns_arr["records"]=array();

    // retrieve our table contents
    // fetch() is faster than fetchAll()
    // http://stackoverflow.com/questions/2770630/pdofetchall-vs-pdofetch-in-a-loop
    while ($row = $stmt->fetch(PDO::FETCH_ASSOC)){
        // extract row
        // this will make $row['name'] to
        // just $name only
        extract($row);

        $racun_item=array(
            "racunId" => $RACUNID,
            "userId" => $USERID,
            "broj" => $BROJ,
            "datum" => $DATUM,
            "vrednost" => $VREDNOST,
            "vrsta" => $VRSTA
        );

        array_push($racuns_arr["records"], $racun_item);
    }

    echo json_encode($racuns_arr);
}

else{
    echo json_encode(
        array("message" => "Nothing found.")
    );
}
?>