oracle数据库中为已经存在表的主键ID设置自增

1. 创建一张表

create table t_user(
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. 为这个表创建序列

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

3. 创建一个触发器

create or replace trigger t_user_tr
before insert on t_user
for each row
begin
select t_user_seq.nextval into :new.user_id from dual;
end t_user_tr;

4. 测试

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