MySQL fetch命令不返回数据

Want the PHP script to pull all data from the database and display it on screen. But can't find the most efficient method to display the records without using the $query_params variable as it generates an error with the parameters in but cannot run without an array?

//initial query
$query = "Select * FROM tbl_data";

//execute query
try {
$stmt   = $db->prepare($query);
$result = $stmt->execute($query_params);
}
catch (PDOException $ex) {
$response["success"] = 0;
$response["message"] = "Database Error!";
die(json_encode($response));
}

And here is the display code

$rows = $stmt->fetchAll();
if ($rows) {
$response["success"] = 1;
$response["message"] = "Post Available!";
$response["posts"]   = array();

foreach ($rows as $row) {
    $post             = array();
    $post["username"] = $row["username"];
    $post["title"]    = $row["title"];
    $post["message"]  = $row["message"];

I would be really grateful if you could help, thank you!