INSERT INTO b (b_num, created) VALUES ( 123 , '15.01.03');
INSERT INTO b (b_num, created) VALUES ( 123 , '16.01.03');

INSERT INTO b (b_num, created) VALUES ( 123 , '15.01.02');
INSERT INTO b (b_num, created) VALUES ( 123 , '15.01.03');

SQL> create unique index pk_b on b (b_num, trunc(created,'YYYY'));

Index created.

create unique index pk_b on b (b_num, trunc(created,'YYYY'))
                                                              *
ошибка в строке  1 :
ORA- 02070 : база данных  не поддерживает this date function в этом контексте

ORA- 02070  database stringstring does not support string in this context

Cause: The remote database does not support the named capability in the context in which it is used.

Action: Simplify the SQL statement. 

CREATE UNIQUE INDEX idx_b ON b (b_num, TRUNC(created,'YYYY'));
                                                     *
ошибка в строке  1 :
ORA- 02070 : база данных  не поддерживает this date function в этом контексте

CREATE OR REPLACE FUNCTION year (adate DATE) RETURN DATE DETERMINISTIC IS
BEGIN
  RETURN trunc(adate,'YYYY');
END year;
/

CREATE UNIQUE INDEX idx_b ON b (b_num, year(created)); 

Индекс создан.

ALTER TABLE b ADD CONSTRAINT pk_b PRIMARY KEY (band_num, year(created))
                                                              *
ошибка в строке  1 :
ORA- 00907 : отсутствует правая скобка

INSERT INTO b(b_num, created) VALUES( 123 , sysdate);

 1  строка создана.
INSERT INTO b(b_num, created) VALUES( 123 ,  sysdate+ 1 );
INSERT INTO b(b_num, created) VALUES( 123 ,  sysdate+ 1 )
            *
ошибка в строке  1 :
ORA- 00001 : нарушено ограничение уникальности (IDX_B)

CREATE OR REPLACE TRIGGER trg_b_ins BEFORE INSERT
ON b FOR EACH ROW  --WHEN (new.b_id=0 OR new.b_id IS NULL)
 
BEGIN
  SELECT seq_b_id.nextval INTO :new.b_id FROM dual;
END trg_b_ins;
/