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; 
/

create or replace type keys_nt is table of number;
/

create or replace function get_keys_tab ( keys_cur sys_refcursor ) 
  return keys_nt pipelined as
  keys keys_nt;
begin

  loop
    fetch keys_cur 
    bulk collect into keys
    limit 100;
    
    exit when keys.count = 0;
    
    for ky in 1 .. keys.count loop
      pipe row ( keys ( ky ) );
    end loop;
    
  end loop;
  
end get_keys_tab;
/


select * from table ( get_keys_tab ( get_keys ) );

COLUMN_VALUE   
           1 
           2 

select * from accounts where account_key not in ( 
  select * from table ( get_keys_tab ( get_keys ) ) 
); 

ACCOUNT_KEY   LAST_NAME   
3             BCD