查询分组数据指行条件满足的行的上一条记录的技巧

--------------------------------------------------------------------------
-- Author : htl258(Tony)
-- Date : 2010-03-26 11:01:09
-- Version:Microsoft SQL Server 2008 (SP1) - 10.0.2531.0 (Intel X86)
-- Mar 29 2009 10:27:29
-- Copyright (c) 1988-2008 Microsoft Corporation
-- Developer Edition on Windows NT 5.1 <X86> (Build 2600: Service Pack 2)
--------------------------------------------------------------------------
--> 生成测试数据表:tb

IF NOT OBJECT_ID('[tb]') IS NULL
DROP TABLE [tb]
GO
CREATE TABLE [tb]([A] NVARCHAR(10),[B] NVARCHAR(10),[C] NVARCHAR(10))
INSERT [tb]
SELECT '00001','01','aaa' UNION ALL
SELECT '00001','02','bbb' UNION ALL
SELECT '00002','01','www' UNION ALL
SELECT '00002','02','yyy' UNION ALL
SELECT '00002','03','ttt' UNION ALL
SELECT '00002','04','bbb'
GO
--SELECT * FROM [tb]

-->SQL查询如下:

declare @c nvarchar(10)
set @c='bbb'

select a,b,c=(select top 1 c from tb where a=t.A and b<t.B order by b desc)
from tb t
where c='bbb'
/*
a b c
---------- ---------- ----------
00001 02 aaa
00002 04 ttt

(2 行受影响)
*/