reusing a constraint while creating a table
===

While creating a table how can I reuse a constraint that has been mentioned for a previous column .  

create table ticket_details(
from_stn char(3) constraint chk check(from_stn in ('vsh','mas','ndl')) constraint nn NOT NULL,
to_stn char(3) constraint nn1 NOT NULL,(instead of crea)
seat_no number(3) constraint PK primary key,
); 