CREATE TABLE test (
    id NUMBER PRIMARY KEY,
    description VARCHAR(1000),
    created DATE,
    superuser_username VARCHAR(16) NOT NULL,
    subject_subjectCode VARCHAR(32) NOT NULL,
    bookey INTEGER,
    CONSTRAINT test_superuser_fkey FOREIGN KEY (superuser_username) REFERENCES superuser (username),
    CONSTRAINT test_subject_fkey FOREIGN KEY (subject_subjectCode) REFERENCES subject (subjectCode),
    CONSTRAINT test_test_fkey FOREIGN KEY (bookey) REFERENCES test (id)
);

CREATE SEQUENCE test_seq
START WITH 1
INCREMENT BY 1;

CREATE TRIGGER test_trigger
BEFORE INSERT ON test
FOR EACH ROW
WHEN (new.id IS null)
BEGIN
  SELECT test_seq.nextval INTO :new.id FROM dual;
END test_trigger