PROMPT Creating Table 'ITEM' with auto-increment primary key 'ID'

BEGIN
  EXECUTE IMMEDIATE 'DROP TABLE item';
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -942 THEN
      RAISE;
    END IF;
END;

CREATE TABLE item
  (
    id      NUMBER(6) NOT NULL,
    name    VARCHAR2(100) NOT NULL,
    sell_in NUMBER(6) NOT NULL,
    quality NUMBER(6) NOT NULL
  );
/

ALTER TABLE item ADD (
  CONSTRAINT item_pk PRIMARY KEY (ID));
/

BEGIN
  EXECUTE IMMEDIATE 'DROP SEQUENCE item_id_seq';
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE != -2289 THEN
      RAISE;
    END IF;
END;

CREATE SEQUENCE item_id_seq
  INCREMENT BY 1
  START WITH 1
  MAXVALUE 999999
  MINVALUE 1
  NOCYCLE;
/

CREATE OR REPLACE TRIGGER item_bis_trg
  BEFORE INSERT ON item
  FOR EACH ROW
BEGIN
    SELECT item_id_seq.NEXTVAL INTO :new.id FROM dual;
END;
/

SHOW ERRORS;