Protect against SQL Injection in PHP [duplicate]

This question already has an answer here:

• How can I prevent SQL-injection in PHP? 28 answers

Im having a little trouble with a basic PHP website that is vulnerable to SQL injection.

Is there a fast simple way to update the below code to prevent this?

I was able to log on to the members area with a simple Boolean SQL expression.

The code is:

 $username = $_POST['username'];
$password = md5($_POST['password']);

 $checklogin = mysql_query("SELECT * FROM users WHERE Username = '".$username."' AND Password = '".$password."'");

if(mysql_num_rows($checklogin))
{
     $row = mysql_fetch_array($checklogin);
    $email = $row['EmailAddress'];

    $_SESSION['Username'] = $username;
    $_SESSION['EmailAddress'] = $email;
    $_SESSION['LoggedIn'] = 1;

     echo "<h1>Success</h1>";
    echo "<p>We are now redirecting you to the member area.</p>";
    echo "<meta http-equiv='refresh' content='2;index.php' />";

Thanks in advance

Wayne