SQL Server设置主键自增长列(使用sql语句实现)

1.新建一数据表，里面有字段id，将id设为为主键

create table tb(id int,constraint pkid primary key (id))
create table tb(id int primary key )

2.新建一数据表，里面有字段id，将id设为主键且自动编号

create table tb(id int identity(1,1),constraint pkid primary key (id))
create table tb(id int identity(1,1) primary key )

3.已经建好一数据表，里面有字段id，将id设为主键

alter table tb alter column id int not null
alter table tb add constraint pkid primary key (id)

4.删除主键

declare @pk varchar(100);
select @pk=name from sysobjects where parent_obj=object_id('tb') and xtype='pk';
if @pk is not null
exec('alter table tb drop '+ @pk)