begin work isolation level serializable;

update t01 set c1 = c0;

commit;

create or replace function my_test() returns integer as $$
declare
   rowcnt   integer;
   asrcnt   integer;
   cur   record;
begin
   rowcnt :=  0 ;
   asrcnt :=  0 ;

   for cur in  select c0, c1 from t01 order by c0
   loop
      if cur.c0 != cur.c1 then
         asrcnt := asrcnt +  1 ;
      end if;
      
      update t01 set c1 = cur.c0 +  2   where c1 = cur.c0 +  1 ;
      rowcnt := rowcnt +  1 ;
   end loop;

   return asrcnt;
end ;
$$ language plpgsql;

begin work isolation level serializable;

select my_test();

commit;

drop function my_test();