PHP PDO query execution don't save passed data - php

Question

I've a problem with PDO prepared statements using mysql.
When the query is executed it will save into the preposed table the placeholders that I've binded using the bindParam() method.
Here is the code and here is a screen of the result of the execution of the query. How i can solve this embaracing problem? I'm a newbie on PDO!
PHP (This is the controller that is called using ajax).
if(isset($_POST['code'])){
$code = filter_var($_POST['code'],FILTER_SANITIZE_STRING);
$qty = filter_var($_POST['quantity'],FILTER_SANITIZE_STRING);
$brand = filter_var($_POST['brand'],FILTER_SANITIZE_STRING);
$article_name = filter_var($_POST['artName'],FILTER_SANITIZE_STRING);
$price = filter_var($_POST['price'],FILTER_SANITIZE_STRING);
$article_type = filter_var($_POST['artType'],FILTER_SANITIZE_STRING);
$note = filter_var($_POST['note'],FILTER_SANITIZE_STRING);
$save = $core->insert_article($code,$qty,$brand,$article_name,$price,$article_type,$note);
if($save){
echo 'ok';
} else {
echo 'error';
}
}
PHP 2 (this is the function of the class who manage all the database operations)
public function insert_article($code,$qty,$brand,$article_name,$price,$article_type,$note){
$db = $this->init_db();
$sql = "INSERT INTO products (cod_articolo, pezzi_disponibili, marca, nome_articolo, prezzo, tipologia_articolo, note) VALUES (':cod_articolo',':pezzi_disponibili',':marca',':nome_prodotto',':prezzo',':tipologia_articolo',':note')";
$stmt = $db->prepare($sql);
$stmt->bindParam(':cod_articolo',$code,PDO::PARAM_STR);
$stmt->bindParam(':pezzi_disponibili',$qty,PDO::PARAM_STR);
$stmt->bindParam(':marca',$brand,PDO::PARAM_STR);
$stmt->bindParam(':nome_articolo',$article_name,PDO::PARAM_STR);
$stmt->bindParam(':prezzo',$price,PDO::PARAM_STR);
$stmt->bindParam(':tipologia_articolo',$article_type,PDO::PARAM_STR);
$stmt->bindParam(':note',$note,PDO::PARAM_STR);
if($stmt->execute()){
echo 'ok';
} else {
echo 'error';
}
}
This is the screen of the results after that the query is executed
table after query execution

Answer 1

Try removing the single quotes surrounding the binding part
$sql = "INSERT INTO products (cod_articolo, pezzi_disponibili, marca, nome_articolo, prezzo, tipologia_articolo, note) VALUES (:cod_articolo,:pezzi_disponibili,:marca,:nome_prodotto,:prezzo,:tipologia_articolo,:note)";