oracle主键自增

create table tb_student
(
id NUMBER(10) not null,
createtime DATE not null,
constraint PK_tb_student primary key (id)           ----主键约束
);

---注释
comment on table tb_student is
'学生表';

comment on column tb_student.id is
'主键id';

comment on column tb_student.createtime is
'创建时间';

--创建序列
create sequence seq_tb_student
minvalue 1
nomaxvalue
start with 1
increment by 1
nocycle --一直累加，不循环
--nocache; --不缓存
cache 10; --缓存10条

--创建触发器，如果insert语句不指定ID自动插入增长值
CREATE OR REPLACE TRIGGER tr_tb_student
BEFORE INSERT ON tb_student FOR EACH ROW WHEN (new.id is null)
begin
select seq_tb_student.nextval into:new.id from dual;
end;