Function: Change data while walking through records

Hi,

I keep having this need to create a function that will change the row data
as I am walking through the data. For example, I process each row in order,
if column1 change from previous row, set column2 to true.

Is this possible?  I can run another query to modify the data, but that
doesn't seem that efficient?

Thanks for any help.

--

An example:

--Simple table
create table tmp1 (
  id integer,
  time timestamp,
  sequential boolean);

insert into tmp1 values (1, '2008-01-01 12:00:00', false),(2, '2008-01-02
12:00:00', false),(3, '2008-01-03 12:00:00', false),(4, '2008-01-08
12:00:00', false),(5, '2008-01-09 12:00:00', false),(6, '2008-01-10
12:00:00', false),(7, '2008-01-15 12:00:00', false),(8, '2008-01-22
12:00:00', false),(9, '2008-01-23 12:00:00', false),(10, '2008-01-25
12:00:00', false);

-- I want line: "my_sequential := true;" to effect that table
CREATE OR REPLACE FUNCTION setseq() RETURNS INTEGER AS
$BODY$
DECLARE
  my_id integer;
  my_time integer;
  my_sequential boolean;
  old_time integer;
  change_count integer;
BEGIN
  change_count := 1;

  for my_id,my_time,my_sequential in
    select id,extract(day from time),sequential from tmp1 order by time
  LOOP
    if (old_time is not null) then
      if (old_time+1 = my_time) then
        my_sequential := true;  --How do I make this work?
        change_count := change_count+1;
      end if;
    end if;
    old_time := my_time;
  END LOOP;
  return change_count;
END;
$BODY$
  LANGUAGE 'plpgsql';
--
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