序列介绍 db官方例子

创建序列

create sequence my_sequence start with 1;

创建序列后，您可以使用 CURRVAL 伪列（返回序列的当前值）或 NEXTVAL 伪列（递增序列并返回新值）在 SQL 语句中访问其值

select my_sequence.NEXTVAL

from dual;

select my_sequence.CURRVAL

from dual;

在触发器中引用序列

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最常见的用途是从触发器内填充表主键值。下面的示例创建一个表并使用触发器填充主键。

create sequence simple_employees_seq;

create table SIMPLE_EMPLOYEES ( 

  empno             number primary key, 

  name              varchar2(50) not null, 

  job               varchar2(50)

  );

没弄过这块 

create or replace trigger SIMPLE_EMPLOYEES_BIU_TRIG

    before insert or update on SIMPLE_EMPLOYEES

    for each row

begin

    if inserting and :new.empno is null then

        :new.empno := simple_employees_seq.nextval;

    end if;

end;

/

 测试触发序列

insert into simple_employees (name, job) values ('Mike', 'Programmer');

insert into simple_employees (name, job) values ('Taj', 'Analyst');

insert into simple_employees (name, job) values ('Jill', 'Finance');

insert into simple_employees (name, job) values ('Fred', 'Facilities');

insert into simple_employees (name, job) values ('Sabra', 'Programmer');

commit;

查看 EMPNO 列是如何填充的

select empno, name, job

from simple_employees

order by 1