Change primary key in Postgres 7.3?

Greetings. We're running Postgres 7.3 on an Intel linux box (Redhat
Enterprise server, version 3.0). We find ourselves in an awkward
position: we have a database of attributes relating to students that
uses as its primary key the ID number of the student. This is awkward
for the following reasons.

Our university used to use social-security numbers for student ID's.
They stopped doing that a few years ago, but didn't force the change on
existing students. Recently they've made a forced, retroactive change
such that ALL students, past and present, now have a student ID that's
not related to social-security number.

I think this a well-justified change, but, unfortunately for us, it
makes many of the primary keys in our database invalid. This problem is
compounded by the fact that the programmer that set up our Postgres
databases has moved on to another job.

Our current programmer would like to start from scratch, redefine the
schema, rebuild the database, etc. Unfortunately, there are a number of
high-profile applications that depend on the database, and many of them
would surely get broken by this kind of transition.

We expect that we WILL eventually rebuild the database, but right now
we're looking for a quick fix. Our current programmer tells me that he
can't find a way to simply change the primary key "in place" in Postgres.

Is there a way to do this?

Thanks.

- Mike
--
Michael Hannon mailto:hannon(at)physics(dot)ucdavis(dot)edu
Dept. of Physics 530.752.4966
University of California 530.752.4717 FAX
Davis, CA 95616-8677