oracle数据库中为已经存在表的主键ID设置自增

1. 建立一张表

create table t_(
user_id number not null primary key,
user_name varchar2(30),
credits number,
user_password varchar2(32),
last_visit date,
last_ip varchar2(23)
)

2. 为这个表建立序列

create sequence T_SEQ
minvalue 1
maxvalue 999999999999999999999999999
start with 21
increment by 1
cache 20;

3. 建立一个触发器

create or replace trigger ttr
before insert on t
for each row
begin
select t_seq.nextval into :new.id from dual;
end t_tr;

4. 测试

insert into t_user values(null,’xiaoming’,123,’111’,sysdate,’192.168.37.132’);
insert into t_user values(6,’xiaoming’,124,’111’,sysdate,’192.168.37.132’);
select * from t_user