Hi guys,
Okay,I think the assumption that I used in my expalnation was not clear cut. It's quite different from the actual scenario. I was thinking that it will be the same.

Okay this is the exact scenario:
I have a table called EMP and has a column called activity_id.
I did a desc on the table and I got this for activity_id

NAME NULL? TYPE
activity_id varchar2(8)

Okay now I want to alter the table so that, the default value for activity_id to be 000, if nothing is entered
in the activity_id column.

I'm sure it's clear now, any help?