求SQL语句 - MS-SQL Server / 疑难问题

表
进货日期, 物品
2010-02-01 白菜
2010-02-02 香菇
2010-02-01 大米
2010-03-01 白菜
2010-03-02 大米
2010-04-01 香菇


要求显示超过(即当前日期-最后进货日期>20)20天的未进货的物品.Sql 语句如何写?

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SQL code:
select [进货日期],[物品]
from [表] where
datediff(day,[进货日期],getdate())>20

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SQL code:
select * from tb where datediff(dd,进货日期,getdate())>20

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SQL code:
--------------------------------------------------------------------------
-- Author : htl258(Tony)
-- Date : 2010-04-26 17:08:16
-- Version:Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86)
-- Jul 9 2008 14:43:34
-- Copyright (c) 1988-2008 Microsoft Corporation
-- Developer Edition on Windows NT 5.1 <X86> (Build 2600: Service Pack 3)
-- Blog : http://blog.csdn.net/htl258
--------------------------------------------------------------------------
--> 生成测试数据表:tb

IF NOT OBJECT_ID('[tb]') IS NULL
DROP TABLE [tb]
GO
CREATE TABLE [tb]([进货日期] DATETIME,[物品] NVARCHAR(10))
INSERT [tb]
S