CREATE TABLE ACCOUNTS 
   (	ACCOUNT_KEY VARCHAR2(20 BYTE),  
	LAST_NAME VARCHAR2(20 BYTE) 
   )

INSERT INTO ACCOUNTS VALUES ( '1', 'AAA' );
INSERT INTO ACCOUNTS VALUES ( '2', 'ABC' );
INSERT INTO ACCOUNTS VALUES ( '3', 'BCD' );

create or replace FUNCTION get_keys 
  RETURN SYS_REFCURSOR 
IS 
  l_rc SYS_REFCURSOR; 
BEGIN 
  OPEN l_rc 
   FOR SELECT account_key         FROM accounts WHERE last_name LIKE 'A%'; 
  RETURN l_rc; 
END; 

SELECT * FROM accounts WHERE account_key NOT IN ( get_keys );