csae when 多条件判断
col1          col2              col3 
a               t                   1
a               s                  2
a               b                  1
b                t                  2
b               b                   3
b               s                   4

判断 如果col1 = a   col2 = t   那么col3值替换为0
结果
col1          col2              col3 
a               t                   0
a               s                  2
a               b                  1
b                t                  2
b               b                   3
b               s                   4
------解决方案--------------------

----------------------------------------------------------------

-- Author  :DBA_HuangZJ(发粪涂墙)

-- Date    :2014-04-08 13:05:22

-- Version:

--      Microsoft SQL Server 2008 R2 (RTM) - 10.50.1600.1 (X64) 

--	Apr  2 2010 15:48:46 

--	Copyright (c) Microsoft Corporation

--	Enterprise Edition (64-bit) on Windows NT 6.2 <X64> (Build 9200: ) (Hypervisor)

--

----------------------------------------------------------------

--> 测试数据[huang]

if object_id('[huang]') is not null drop table [huang]

go 

create table [huang]([col1] nvarcha