Safe, Simple, SQL statement

[Dankinit]

After reading about sql injection methods on various sites and proper coding techniques from the new vb3 manual, I'm looking over all my code before launching next vb3 version of my site.

What's the proper way to write this statement? As it stands, it doesn't work. I know it's the way i'm using quotes around $letter variable, just wondering the "proper" and safe way to access this. Thanks for any help

PHP Code:

    $letterlisting = $DB_site->query("
        SELECT ID,Artist 
        FROM music 
        WHERE Artist LIKE '" . $letter . "'
        GROUP BY Artist 
        ORDER BY Artist;
    ");