auto datetime update on UPDATE?

Hi,

i have set up a table, where two fields (creation_dt and modification_dt)
always get the actual date/time by default when doing an INSERT.
my question is, how is it possible to let the field modification_dt
change when doing an UPDATE?
Is there a way to solve it in SQL?

(actually i found something in the mailing list archive,
where the sender solves the problem by creating a trigger
and a C function, but i would really apppreciate if there was
a solution in SQL only.
anyway, that solution is at
http://www.PostgreSQL.ORG/mhonarc/pgsql-sql/1998-06/msg00056.html )

Zsolt Tulassay

ps i'm not on the mailing list so please send a copy to my address
as well. thanks