结果集合并，想了一天没整出来。
表合并 sql?server 数据库 join
[解决办法]
select t.cc,t.s,isnull(A.a,0)as A_Amout,isnull(B.a,0)as B_Amout,isnull(C.a,0)as C_Amout
(select cc,s from A union select cc,s from B union select cc,s from C )t
left join A on a.cc=t.cc and a.s=t.s
left join B on b.cc=t.cc and b.s=t.s
left join C on c.cc=t.cc and c.s=t.s
[解决办法]

----------------------------
-- Author  :DBA_Huangzj()
-- Date    :2013-03-07 17:25:35
-- Version:
--      Microsoft SQL Server 2008 R2 (SP1) - 10.50.2500.0 (X64) 
--Jun 17 2011 00:54:03 
--Copyright (c) Microsoft Corporation
--Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1, v.721)
--
----------------------------


--> 测试数据：[A]
if object_id('[A]') is not null drop table [A]
go 
create table [A]([cc] varchar(2),[s] varchar(1),[a] numeric(4,1))
insert [A]
select 'C1','a',235.4 union all
select 'C1','b',88 union all
select 'C1','c',34


--> 测试数据：[B]
if object_id('[B]') is not null drop table [B]
go 
create table [B]([cc] varchar(2),[s] varchar(1),[a] int)
insert [B]
select 'C1','a',11 union all
select 'C1','b',22 union all
select 'C1','d',33


--> 测试数据：[C]
if object_id('[C]') is not null drop table [C]
go 
create table [C]([cc] varchar(2),[s] varchar(1),[a] int)
insert [C]
select 'C1','a',2000 union all
select 'C1','b',500


--------------开始查询--------------------------


SELECT COALESCE(a.cc,b.cc,c.cc) AS cc,COALESCE(a.s,b.s,c.s) AS s,ISNULL(a.a,0),ISNULL(b.a,0),ISNULL(c.a,0)
FROM a full JOIN b ON a.cc=b.cc AND a.s=b.s
full JOIN c ON a.cc=c.cc AND a.s=c.s
----------------结果----------------------------
/* 
cc   s                                                         
 
---- ---- --------------------------------------- ----------- -----------
C1   a    235.4                                   11          2000
C1   b    88.0                                    22          500
C1   c    34.0                                    0           0
C1   d    0.0                                     33          0
*/