表定义：

CREATE TABLE departments (
  ID           NUMBER(10)    NOT NULL,DESCRIPTION  VARCHAR2(50)  NOT NULL);

ALTER TABLE departments ADD (
  CONSTRAINT dept_pk PRIMARY KEY (ID));

CREATE SEQUENCE dept_seq START WITH 1;

触发器定义：

CREATE OR REPLACE TRIGGER dept_bir 
BEFORE INSERT ON departments 
FOR EACH ROW

BEGIN
  SELECT dept_seq.NEXTVAL
  INTO   :new.id
  FROM   dual;
END;
/

更新：IDENTITY列现在可用于Oracle 12c版本see this：

CREATE TABLE t1 (c1 NUMBER GENERATED BY DEFAULT ON NULL AS IDENTITY,c2 VARCHAR2(10));

或指定开始和增加值，也阻止任何插入标识列(GENERATED ALWAYS)(再次，仅Oracle 12c)

CREATE TABLE t1 (
    c1 NUMBER GENERATED ALWAYS AS IDENTITY (START WITH 1 INCREMENT BY 1),c2 VARCHAR2(10)
);