Create table with auto increment using ORACLE

Table defination :

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

-- alter table to add primary key
ALTER TABLE departments ADD (
CONSTRAINT dept_pk PRIMARY KEY (ID));

-- create sequence
CREATE SEQUENCE dept_seq;

Trigger defination :

-- create trigger to +1 at sequence number
CREATE OR REPLACE TRIGGER dept_bir
BEFORE INSERT ON departments
FOR EACH ROW

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