【SQL 编程你也行】SQL Server 2014新功能之序列Sequence

在SQL Server中提供了 identity关键字，在创建表的时候指定，可以让某列实现自动增长。

而在SQL Server 2014中新增了序列Sequence，通过这个序列，不仅可以实现单表的某列的增长，还可以实现多表中的某列的自动增长。

下面是一个例子：

1、创建表、创建序列

drop sequence dbo.sequence_test



create sequence dbo.sequence_test
as int
start with 1
increment by 1;


if object_id('test') is not null
   drop table test;


create table test 
(
id int primary key,
name varchar(20),
num int
);

insert into test(id,name,num)
values(next value for dbo.sequence_test,'a',10);


insert into test(id,name,num)
values(next value for dbo.sequence_test,'b',20),
      (next value for dbo.sequence_test,'c',30),
      (next value for dbo.sequence_test,'d',40);


select * from test  

2、使用序列

declare @n int


set @n = next value for dbo.sequence_test;


insert into test(id,name,num)
values(@n,'b',20);




select  next value for dbo.sequence_test --6




declare @n int


set @n = next value for dbo.sequence_test;  --7


insert into test(id,name,num)
values(@n,'b',20);



select * from test  

3、在多个表使用序列

if object_id('test1') is not null
   drop table test1;


create table test1 
(
id int primary key,
name varchar(20),
num int
);



insert into test1(id,name,num)
values(next value for dbo.sequence_test,'a',10);


insert into test1(id,name,num)
values(next value for dbo.sequence_test,'111111111111111111111111111111111',10);  --由于超出了定义长度,所以报错,但序列值会继续递增到下一个


insert into test1(id,name,num)
values(next value for dbo.sequence_test,'a',10);


select * from test


select * from test1

4、在结果集中生成重复序列号

if object_id('sequence_tinyint') is not null
   drop sequence sequence_tinyint
go


create sequence dbo.sequence_tinyint
as tinyint
	start with 1
	increment by 1
	minvalue 1
	maxvalue 2
	cycle
go


--发现值是一样的
select next value for dbo.sequence_tinyint, --1
       next value for dbo.sequence_tinyint


select next value for dbo.sequence_tinyint   --2


select next value for dbo.sequence_tinyint   --1

5、生成序列号

select *,
       next value for dbo.sequence_test over(order by id) as 连续的id
from test


--注意:再次运行,值又发生变化了
select *,
       next value for dbo.sequence_test over(order by id) as 连续的id
from test

6、重置序列号

alter sequence dbo.sequence_test
restart with 1;


--有从1开始
select next value for dbo.sequence_test;

7、将表从标识更改为序列

if object_id('ggg') is not null
   drop table ggg;


create table ggg
(
id int identity(1,1) not null,
name varchar(10)
constraint pk_ggg_id primary key clustered (id)
);


insert into ggg(name)
values('a'),
      ('b'),
      ('c');
      


alter table ggg
add id_new int null


update ggg set id_new = id;


alter table ggg
drop constraint pk_ggg_id;


alter table ggg
drop column id


exec sp_rename 'dbo.ggg.id_new','id','column';


alter table ggg
alter column id int not null;


alter table ggg
add constraint pk_ggg_id primary key clustered(id);



alter table ggg
add constraint df_ggg_id default( next value for dbo.sequence_test) for id;


select next value for dbo.sequence_test



insert into ggg(name,id)
values('d',default)


select * from ggg