1、创建一个表
create table t_client (id number(4) primary key,
pid number(4) not null,
name varchar2(30) not null,
client_id varchar2(10),
client_level char(3),
bank_acct_no varchar2(30),
contact_tel  varchar2(30),
address    varchar2(30),
zip_code varchar2(10),
is_leaf char(1) default ‘y‘ check (is_leaf in(‘y‘,‘n‘)),
is_client char(1) default ‘n‘ check (is_client in(‘y‘,‘n‘)
)); 

create sequence seq_t_client_id
minvalue 1
maxvalue 99999999
start with 1
increment by 1
nocache
order;

CREATE OR REPLACE TRIGGER trg_t_client_id
BEFORE INSERT ON Users
FOR EACH ROW
BEGIN
SELECT  seq_t_client_id.nextval INTO :new.id FROM dual;
END;