--try
SELECT b.[A],a.[B]
FROM   (
     SELECT CONVERT(VARCHAR(6) , DATEADD(mm , number , '20071101') , 112) AS [B]
     FROM   master..spt_values
     WHERE  type = 'p'
            AND number BETWEEN 0 AND DATEDIFF(mm , '20071101' , GETDATE())
    ) a
CROSS JOIN (
         SELECT [A]  FROM [tb] GROUP BY [A]
        ) b
EXCEPT 
SELECT * FROM   [tb]

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

-->try
declare @test table(A int,B int)
insert into @test
select 1, 201208 union all
select 2, 201208 union all  
select 3, 201205 union all
select 1, 201207 union all
select 2, 201206 union all
select 3, 201204 union all
select 1, 201203 union all
select 2, 201204 union all
select 3, 201201

declare @ym int
set @ym=200711
select * from
(
    select t.A,convert(varchar(6),dateadd(mm,number,ltrim(@ym)+'01'),112) dt 
    from master..spt_values,(select distinct A from @test) t 
    where type='P' 
    and number<=datediff(mm,ltrim(@ym)+'01',getdate())
) a
where not exists(select 1 from @test where B=a.dt and A=A.A)
order by A,dt
/*
A           dt
----------- ------
1           200711
1           200712
1           200801
1           200802
1           200803
1           200804
1           200805
1           200806
1           200807
1           200808
1           200809
1           200810
1           200811
1           200812
1           200901
1           200902
1           200903
1           200904
1           200905
1           200906
1           200907
1           200908
1           200909
1           200910
1           200911
1           200912
1           201001
1           201002
1           201003
1           201004
1           201005
1           201006
1           201007
1           201008
1           201009
1           201010
1           201011
1           201012
1           201101
1           201102
1           201103
1           201104
1           201105
1           201106
1           201107
1           201108
1           201109
1           201110
1           201111
1           201112
1           201201
1           201202
1           201204
1           201205
1           201206
1           201209
2           200711
2           200712
2           200801
2           200802
2           200803
2           200804
2           200805
2           200806
2           200807
2           200808
2           200809
2           200810
2           200811
2           200812
2           200901
2           200902
2           200903
2           200904
2           200905
2           200906
2           200907
2           200908
2           200909
2           200910
2           200911
2           200912
2           201001
2           201002
2           201003
2           201004
2           201005
2           201006
2           201007
2           201008
2           201009
2           201010
2           201011
2           201012
2           201101
2           201102
2           201103
2           201104
2           201105
2           201106
2           201107
2           201108
2           201109
2           201110
2           201111
2           201112
2           201201
2           201202
2           201203
2           201205
2           201207
2           201209
3           200711
3           200712
3           200801
3           200802
3           200803
3           200804
3           200805
3           200806
3           200807
3           200808
3           200809
3           200810
3           200811
3           200812
3           200901
3           200902
3           200903
3