学步园

create table test
(pid integer primary key,
  name varchar(20)
  );
  
  select * from test;
  insert into test values(1,'Jack');

create sequence test_seq;--创建序列
select test_seq.nextval from dual;--每次使用后序列加一
select test_seq.currval from dual;--查询当前序列的值
insert into test values(test_seq.nextval,'Jack Or Duck?');--序列的使用
drop sequence test_seq;--删除序列
create sequence test_seq start with 8;--指定序列的初始值
alter sequence test_seq minvalue 9;--设置序列的最小值
alter sequence test_seq maxvalue 9999;--设置序列的最大值
alter sequence test_seq increment by 1;--设置序列的步长
drop sequence test_seq_1;
create sequence test_seq_1 start with 3 minvalue 1 maxvalue 30 increment by 1;
select test_seq_1.nextval from dual;
alter sequence test_seq_1 cycle;
alter sequence test_seq_1 nocycle;--关闭循环取值功能
alter sequence test_seq_1 cache 10;

--设置序列缓存大小的作用，注:序列缓存默认为20
create sequence test_seq_2 start with 1 minvalue 1 maxvalue 20 increment by 3;
alter sequence test_seq_2 cycle;

--上述语句会报错：Cache值必须小于cycle值

alter sequence test_seq_2 increment by 2;
alter sequence test_seq_2 cycle;
--还是报错
alter sequence test_seq_2 increment by 1;
alter sequence test_seq_2 cycle;
--还是报错
alter sequence test_seq_2 maxvalue 21;
alter sequence test_seq_2 cycle;
--不报错了

--或者修改
alter sequence test_seq_1 cache 5;
--start with 1 and maxvalue 10 step 1 then 10 times cycle and bigger than 5