if object_id('t1') is not null drop table t1 
 go 
create table t1([id1] int,[name1] varchar(10),[cid] int)
insert t1 select 1,'aa',1
union all select 2,'bb',1
union all select 3,'cc',2
go
if object_id('tg') is not null drop trigger tg 
 go 
CREATE trigger tg ON t1 
for insert,update 
as 
if exists(select 1 
          from inserted t
          where cid in(
              select cid 
              from t1 
              group by cid 
              having count(cid)>2)
          )
begin 
  raiserror('您输入的CID不允许超过两条记录',16,1)
  rollback
end     
go   
-->开始测试 
insert t1 select 4,'dd',1
/*
消息 50000，级别 16，状态 1，过程 tg，第 13 行
您输入的CID不允许超过两条记录
消息 3609，级别 16，状态 1，第 1 行
事务在触发器中结束。批处理已中止。
*/
insert t1 select 4,'dd',2
/*
(1 行受影响)
*/
select * from t1
/*
id1         name1      cid
----------- ---------- -----------
1           aa         1
2           bb         1
3           cc         2
4           dd         2

(4 行受影响)
*/

------解决方案--------------------
随手写了一下，你试试
SQL code
------------------------------------
-- Author:  happyflystone  
-- Date  :  2009-04-20 22:29:58
-- Ver:     Microsoft SQL Server 2005 - 9.00.2047.00 (Intel X86) 
--          Apr 14 2006 01:12:25 
--          Copyright (c) 1988-2005 Microsoft Corporation
--          Standard Edition on Windows NT 5.0 (Build 2195: Service Pack 4)
--      
------------------------------------

-- Test Data: T1
IF OBJECT_ID('T1') IS NOT NULL 
    DROP TABLE T1
Go
CREATE TABLE T1(id1 INT,name1 NVARCHAR(2),cid INT)
Go
INSERT INTO T1
SELECT 1,'aa',1 UNION ALL
SELECT 2,'bb',1 UNION ALL
SELECT 3,'cc',2 UNION ALL
SELECT 4,'dd',3 UNION ALL
SELECT 5,'ee',3 UNION ALL