PL/SQL Oracle Dual Table

select * from locations
end;

declare
  v_city locations.city%type;
begin
  select 'Roma'
  into v_city
  from dual;

  dbms_output.put_line('Selected city is; '||v_city);
end;


declare
  v_city locations.city%type;
begin
  select 'Roma'
  into v_city
  from dual;
  update locations
  set city=v_city
  where postal_code='6823';
end;


declare
  v_postal_code locations.postal_code%type;
begin
  select '6823'
  into v_postal_code
  from dual;
  dbms_output.put_line(v_postal_code);
  update locations
  set city='Romaxx'
  where postal_code=v_postal_code;
end;