---启用or禁用指定表所有外键约束 
alter table PUB_STRU  NOCHECK constraint all; 
alter table PUB_STRU  CHECK constraint all; 
   
---生成启用or禁用指定表外键约束的sql 
select 'ALTER TABLE ' + b.name + ' NOCHECK CONSTRAINT ' + a.name +';'  from sysobjects a ,sysobjects b where a.xtype ='f' and a.parent_obj = b.id and b.name='表名'; 
select 'ALTER TABLE ' + b.name + ' CHECK CONSTRAINT ' + a.name +';'  from sysobjects a ,sysobjects b where a.xtype ='f' and a.parent_obj = b.id and b.name='表名'; 
 
--生成的sql如下
ALTER TABLE PUB_STRU NOCHECK CONSTRAINT PUBSTRU_FK1;
ALTER TABLE PUB_STRU NOCHECK CONSTRAINT PUBSTRU_FK2;
ALTER TABLE PUB_STRU CHECK CONSTRAINT PUBSTRU_FK1;
ALTER TABLE PUB_STRU CHECK CONSTRAINT PUBSTRU_FK2;  
 
 --查看约束状态（查询字典表 sys.foreign_keys，该字典表开始出现于sqlserver2005及以上版本）：
select name , is_disabled from sys.foreign_keys order by name; 
 --其中：name  ： 外键约束名称   is_disabled : 是否已禁用

--删除外键
alter table AdItem drop constraint AdOrder_AdItem_FK1
 
--增加外键
alter table AdItem
add constraint AdOrder_AdItem_FK1 foreign key (AI_nOrderNo) references AdOrder(AO_nOrderNo)
 
--单个表的一个外键
alter table Student nocheck constraint FK__Student__SchoolN__4222D4EF 
alter table Student check constraint FK__Student__SchoolN__4222D4EF 
 
--单个表的所有外键
alter table Student nocheck constraint all 
alter table Student check constraint all 
 
--某个数据库的所有表
EXEC sp_MSforeachtable @command1='alter table ?  NOCHECK constraint all;
EXEC sp_MSforeachtable @command1='alter table ?  CHECK constraint all;