if object_id('tb') is not null drop table tb
go
create table tb(col nvarchar(max))
go
insert into tb select 'abc' union all
select 'def'
go
select right('abc',0)   --显示为空
select right('def',0)   --显示为空
select col,right(col,0) from tb  --显示为Null

if object_id('tb') is not null drop table tb
go
create table tb(col nvarchar(max))
go
insert into tb select 'abc' union all
select 'def'
go
select right('abc',0)--显示为空
(无列名)

select right('def',0)   --显示为空
(无列名)

select col,right(col,0) from tb 
/*
col    (无列名)
abc    
def    
*/

我这全为空，没出现null

------解决方案--------------------
楼主是什么环境，以下测试环境是没问题的，结果一致
环境:
SQL code
Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (X64)   Jul  9 2008 14:17:44   Copyright (c) 1988-2008 Microsoft Corporation  Enterprise Evaluation Edition (64-bit) on Windows NT 6.1 <X64> (Build 7600: ) (VM)

------解决方案--------------------
SQL code

declare @a varchar(10)
set @a=N'abc'
select right(@a,0)
select right(convert(nvarchar(max),'def'),0



----


(1 row(s) affected)


----------------------------------------------------------------------------------------------------------------
NULL

(1 row(s) affected)