SELECT'ing a function call

I would like to be able to define a table with 1 column containing user
names,
and the next column being a dynamically generating function that returns a
user's quota.

I think I see how to create the shared object, and the SQL function. But,
how
do I create a table that uses a function for a column based on the value of
another
column.

For example, I tried:

CREATE TABLE test (
num1 INTEGER,
num2 INTEGER DEFAULT add_one('num1')
);

But that said that pg_atoi doesn't understand num1 -- so apprenting atoi is
interpreting
num1 as a string, so I tried ...DEFAULT add_one(num1) which gave a different
error.

Is this even possible? To have a "trigger" based on a select statement. I
looked at the SQL
TRIGGER command and it seems to only work for INSERT, UPDATE and DELETE. I
need a "trigger"
for SELECT's.

Thanks,
Jared H.