怎样修改某一字段为主键?

[阿阳888]

已知有一个student表,其中没有设主键,我想把其中的id 字段设为主键,怎么办呢?
eg: alter table student
alter column id int not null
constraint PK_id primary key
但这样不行!怎么办呢?

[iwl]

ALTER TABLE [dbo].[student] WITH NOCHECK ADD
CONSTRAINT [PK_student] PRIMARY KEY CLUSTERED
(
[ID]
) ON [PRIMARY]
GO

[xinxin20009]

alter table student add
constraint PK_id primary key (id)

[Well]

ALTER TABLE dbo.A1 ADD CONSTRAINT
PK_A1 PRIMARY KEY CLUSTERED
(
ID
) ON [PRIMARY]

[vivianfdlpw]

--添加not null约束
alter table student alter column ID int not null
go
--设置主键
alter table student add constraint con_PK primary key(ID)

[新鲜鱼排]

up

[zouqiang122]

support you...

[新鲜鱼排]

不是很明白，哪位能解釋一下。
我試了一下也不是很好用
Table 'student' already has a primary key defined on it.

[hglhyy]

楼主对SQL语句不熟的话,可以直接到企业管理器选中表右键后 选 设计 来完成 主键的设定

[todouwang]

Table 'student' already has a primary key defined on it.
--说明这个表已经是有主键了撒

[天地客人]

你可以直接在管理器中修改列属性啊!