num_rows keeps returning a null [duplicate] - php

Question

This question already has answers here:
When to use single quotes, double quotes, and backticks in MySQL
(13 answers)
Closed 7 years ago.
I honestly can't see why this doesn't work. I have checked it several times even compared it to other examples I have done that does work. Please note that I have taken it down to the simplest form so there is no sql injection protection. That comes later.
//user real escape string to prevent SQL injection
$username = $_POST['username'];
$password = $_POST['password'];
//check if username and password is blank
if (!$username || !$password)
die ("Not all the fields were filled in");
//Server details
$host = 'localhost';
$user = 'tm_user';
$password = 'password';
//The database name
$database = 'TransportMe';
// Create connection
$con = new mysqli($host, $user, $password, $database);
// Check connection
if ($con->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
//since user and password is not blank, find user info using the email and password entered by user
$sql= "SELECT * FROM Users WHERE 'email'='$username' AND 'password' = '$password';";
//Get the results
$result = $con->query($sql);
//Check if null
if ($result->num_rows == null)
die("Null");

Answer 1

use backticks for columns in your query like this
$sql= "SELECT * FROM Users WHERE `email` = '$username' AND `password` = '$password'";

Answer 2

Your query should be:
//since user and password is not blank, find user info using the email and password entered by user
$sql= "SELECT * FROM `Users` WHERE `email` = '{$username}' AND `password` = '{$password}';";