A history procedure that prevents duplicate entries

Hi all,

   I've been using a procedure to make a copy of data in my public
schema into a history schema on UPDATE and INSERTs.

   To prevent duplicate entries in the history, I have to lead in the
current data, compare it in my program and then decided whether
something has actually changed or not before doing an update. This
strikes me as wasteful coding and something I should be able to do in my
procedure.

   Given the following example tables and procedure, how could I go
about changing it to prevent duplicate/unchanged entries being saved to
the history schema? Even a pointer to a relevant section of the docs
would be appreciated... My knowledge of procedures is pretty weak. :)

Madi

CREATE TABLE radical
(
    rad_id        integer        primary key    default(nextval('id_seq')),
    rad_char    text        not null,
    rad_name    text
);

CREATE TABLE history.radical
(
    rad_id        integer        not null,
    rad_char    text        not null,
    rad_name    text,
    hist_id         integer         not null
default(nextval('hist_seq')),
    modified_date   timestamp       default now()
);

CREATE FUNCTION history_radical() RETURNS "trigger"
    AS $$
    DECLARE
        hist_radical RECORD;
    BEGIN
        SELECT INTO hist_radical * FROM public.radical WHERE rad_id=new.rad_id;
        INSERT INTO history.radical
            (rad_id, rad_char, rad_name)
            VALUES
            (hist_radical.rad_id, hist_radical.rad_char, hist_radical.rad_name);
        RETURN NULL;
    END;$$
LANGUAGE plpgsql;

CREATE TRIGGER trig_radical AFTER INSERT OR UPDATE ON "radical" FOR EACH
ROW EXECUTE PROCEDURE history_radical();