Oracle 中序列使用詳解

 

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

create sequence test_seq;--創建序列
select test_seq.nextval from dual;--每次使用後序列加一
select test_seq.currval from dual;--查詢當前序列的值
insert into test values(test_seq.nextval,'Jack Or Duck?');--序列的使用
drop sequence test_seq;--刪除序列
create sequence test_seq start with 8;--指定序列的初始值
alter sequence test_seq minvalue 9;--設置序列的最小值
alter sequence test_seq maxvalue 9999;--設置序列的最大值
alter sequence test_seq increment by 1;--設置序列的步長
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;--關閉循環取值功能
alter sequence test_seq_1 cache 10;

--設置序列緩存大小的作用，注:序列緩存默認爲20
create sequence test_seq_2 start with 1 minvalue 1 maxvalue 20 increment by 3;
alter sequence test_seq_2 cycle;

--上述語句會報錯：Cache值必須小於cycle值

alter sequence test_seq_2 increment by 2;
alter sequence test_seq_2 cycle;
--還是報錯
alter sequence test_seq_2 increment by 1;
alter sequence test_seq_2 cycle;
--還是報錯
alter sequence test_seq_2 maxvalue 21;
alter sequence test_seq_2 cycle;
--不報錯了

--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