SQL Server设置主键自增长列

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)