$dbh->selectrow_array
	  ( "SELECT UserID, Activeuser, Created, Modified" .
	    " FROM ValidSession" .
	    " WHERE SessionID = ?" .
	    " AND SessionDigest = ?",
	    undef,
	    $sessionid,
	    $sessiondigest );

  # if a row was returned then it was a good match otherwise something is wrong (the session might have just expired as well - views are useful for that)