CRUD Read operation PHP - php

Question

I am creating an Android Application that requires information to be retrieved from a MySQL database on a MAMP server. I have written PHP code to try retrieve the information from the database however there is no information being retrieved from the database. I have checked the code using PHP code checker and there is no issues found. Can anyone find any issues or provide any links to help. Thank you in advance.
<?php
/*
* Following code will list all the products
*/
// array for JSON response
$response = array();
// include db connect class
require_once('connect.php');
// connecting to db
//$db = new db_name();
// get all products from products table
$result = mysqli_query("SELECT * FROM tbl_book");
// check for empty result
if (mysqli_num_rows($result) > 0) {
// looping through all results
// book node
$response["books"] = array();
while ($row = mysqli_fetch_array($result)) {
// temp user array
$book = array();
$book["id"] = $row["id"];
$book["title"] = $row["title"];
$book["description"] = $row["description"];
$book["bookID"] = $row["bookID"];
// push single book into final response array
array_push($response["books"], $book);
}
// success
$response["success"] = 1;
// echoing JSON response
echo json_encode($response);
} else {
// no products found
$response["success"] = 0;
$response["message"] = "No book found";
// echo no users JSON
echo json_encode($response);
}
?>