What are the first names of customers who have not rented any films after '2005-08-23 02:06:01'?
SELECT first_name FROM customer WHERE customer_id NOT IN( SELECT customer_id FROM rental WHERE rental_date  >  '2005-08-23 02:06:01' )
'2005-08-23 02:06:01' sonrasında film kiralamamış müşterilerin ilk isimleri nelerdir?