SQL & PL/SQL

Is it possible to create a default constraint on a table based on some conditional logic.

For example:

CREATE TABLE TEST_T( DEPT_NO NUMBER,

                                      GRANT_FL CHAR(1)

);

DEPT_NO GRANT_FL

10             Y

10             Y

0               N

I want the DEPT_NO to be populated with a default value of 10 only when GRANT_FL = 'Y' Otherwise Set it to 0.

I can do this with a After Insert Trigger but would be better if this can be done via case statement which sets a default value.

Thanks Much!

Kevin