show the customer ids and first names without a credit card
SELECT customer_id ,  customer_first_name FROM Customers EXCEPT SELECT T1.customer_id ,  T2.customer_first_name FROM Customers_cards AS T1 JOIN Customers AS T2 ON T1.customer_id   =   T2.customer_id WHERE card_type_code   =   "Credit"
without a credit card refers to filtering out customers that have a credit card; customer ids and first names refers to selecting customer_id and customer_first_name; EXCEPT is used to subtract the set of customers with a credit card from all customers;