>932
こう言うこと？
create table hoge (i integer, t timestamp default current_timestamp);
hoge=# insert into hoge (i) values (12);
hoge=# select * from hoge;
i | t
----+-------------------------------
12 | 2003-02-20 13:01:45.227974-05
(1 row)

で更新時にtimestamp入れればいいんでないかと？
hoge=# update hoge set i=23, t=current_timestamp where i=12;
UPDATE 1
hoge=# select * from hoge;
i | t
----+-------------------------------
23 | 2003-02-20 13:07:11.440763-05
(1 row)