Oracle创建表ID自增长

CREATE TABLE GENERATEQRCODE(
id int not null,
explain VARCHAR2(100),
qr_code VARCHAR(100),
enddate VARCHAR(100),
user_code VARCHAR(100),
user_code VARCHAR(100)
)
CREATE SEQUENCE GENERATEQRCODE(表名)_ID_SEQ MINVALUE 1 NOMAXVALUE INCREMENT BY 1 START WITH 1 NOCACHE;
CREATE OR REPLACE TRIGGER GENERATEQRCODE(表名)_INS_TRG BEFORE INSERT ON GENERATEQRCODE(表名) FOR EACH ROW WHEN(NEW.ID IS NULL)
BEGIN
SELECT GENERATEQRCODE(表名)_ID_SEQ.NEXTVAL INTO :NEW.ID FROM DUAL;
END;