BuddyPress.org

global $current_blog,$wpdb;

$blog_url = get_blog_option($current_blog->blog_id, 'siteurl' );

$blog_url_pieces = explode("/", $blog_url);

$blog_url = $blog_url_pieces[2];

$site_id = $wpdb->get_var( "SELECT COUNT(*) FROM wp_site WHERE domain='".$blog_url."'");