You should use a sequence to generate keys for your table, perhaps something like this:
Create the sequence:
CREATE SEQUENCE mySequence
MINVALUE 1
MAXVALUE 999999999999999999999999999
START WITH 1
INCREMENT BY 1
CACHE 20;
Use the sequence to generate unique primary keys for the table:
INSERT INTO myTable (id, name)
VALUES (mySequence.nextval, 'Oh my ;-)');
Best regards
Espen Harlinn