adding column with not null constraint

I'm looking to add a column to my database with not null and a default
value:

vk=> alter table msg_owner add column user_optional_fields varchar(255) NOT NULL default '';
ERROR:  Adding columns with defaults is not implemented.       Add the column, then use ALTER TABLE SET DEFAULT.
vk=> alter table msg_owner add column user_optional_fields varchar(255) NOT NULL ;
ERROR:  Adding NOT NULL columns is not implemented.       Add the column, then use ALTER TABLE ADD CONSTRAINT.

Ok, so we can succeed with this:

ALTER TABLE msg_owner ADD COLUMN user_optional_fields VARCHAR(255);
ALTER TABLE msg_owner ALTER user_optional_fields SET DEFAULT '';
UPDATE msg_owner SET user_optional_fields = '';

Now my problem is I cannot find any syntax for ALTER TABLE ADD
CONSTRAINT to put a NOT NULL constraint on a column.  Can someone help
me here?

I'm using Postgres 7.2.1 on FreeBSD 4.6.

Thanks.

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Vivek Khera, Ph.D.                Khera Communications, Inc.
Internet: khera@kciLink.com       Rockville, MD       +1-240-453-8497
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