--删除主键约束

DECLARE @Constraint_Name varchar (200)

select @Constraint_Name = Name from dbo.sysobjects

where Xtype = 'PK' and Parent_Obj =

(select [ID] from dbo.sysobjects

where id = object_id(N'[表名称]')

and OBJECTPROPERTY(id, N'IsUserTable') = 1)

if @Constraint_Name <> ''

begin

alter table 表名称 drop constraint @Constraint_Name

end

--删除主键字段

-- 何问起 hovertree.com 

declare @count int

select @count = count(*) from sysobjects a,syscolumns b

where a.id = b.id and b.name = '主键字段名' and a.Name = '表名称'

if @count > 0

begin

alter table 表名称 drop column 主键字段名

end

--创建字段，主键，并自增

alter table 表名称 add 主键字段名 int identity(1,1) PRIMARY KEY