--> 测试数据：[A1]
if object_id('[A1]') is not null drop table [A1]
create table [A1]([A01] varchar(1),[A02] varchar(6),[A03] varchar(8),[A04] datetime)
insert [A1]
select 'A','ZS0001',null,'20111201' union all
select 'B',null,'ZS0002','20120201' union all
select 'C','ZS0003','ZS0003','20120321' union all
select 'D','ZS0004',null,'20120301' union all
select 'E','ZS0005','ZS0005','20120301'

select [A01] as [B01],
case when [A02] is null then [A03] else [A02] end as [B02],
LTRIM(YEAR([A04])) as [B03],ltrim(MONTH([A04])) as [B04]
from A1

/*
B01    B02    B03    B04
A    ZS0001    2011    12
B    ZS0002    2012    2
C    ZS0003    2012    3
D    ZS0004    2012    3
E    ZS0005    2012    3
*/

------解决方案--------------------

SQL code
create table A(A01 varchar2(20),A02 varchar2(20),A03 varchar2(20),A04 date)

insert into a values('A', 'ZS0001', null     ,to_date('20111201','YYYYMMDD'))

insert into a values('B', null    , 'ZS0002' ,to_date('20120201','YYYYMMDD'))

insert into a values('C', 'ZS0003', 'ZS0003' ,to_date('20120321','YYYYMMDD'))

insert into a values('D', 'ZS0004', null     ,to_date('20120301','YYYYMMDD'))

insert into a values('E', 'ZS0005', 'ZS0005' ,to_date('20120301','YYYYMMDD'))

create table B(B01 varchar2(20),B02 varchar2(20),B03 int,B04 int)

insert into b values('A', 'ZS0001', 2011 ,12)

insert into b values('B', 'ZS0002', 2012 ,2)

insert into b values('C', 'ZS0003', 2012 ,3)

insert into b values('D', 'ZS0004', 2012 ,3)

insert into b values('E', 'ZS0005', 2012 ,3 )

select * from b

--你是只比对月份则如下：
select a.a01, (case when a.a02 = '' and a.a02 is null then a.a03 else a.a02 end) a02_03,to_char(a.a04,'yyyymmdd') a04, b.* from a , b
where trunc(months_between(a.a04,to_date(to_char(b.b03) || LPAD(to_char(b.b04),2,'0') || '01','YYYYMMDD'))) = 1

/*
A01 A02_03 A04      B01 B02    B03  B04
C   ZS0003 20120321 B   ZS0002 2012 2 
D   ZS0004 20120301 B   ZS0002 2012 2 
E   ZS0005 20120301 B   ZS0002 2012 2 

3 rows selected.
*/

--不知道是否是a01-->b01 and a02(a03)-->b02 and 月份也相等，则如下：
select a.a01, (case when a.a02 = '' and a.a02 is null then a.a03 else a.a02 end) a02_03,to_char(a.a04,'yyyymmdd') a04, b.* from a , b
where a.a01 = b.b01 and (case when a.a02 = '' and a.a02 is null then a.a03 else a.a02 end) = b.b02 and
trunc(months_between(a.a04,to_date(to_char(b.b03) || LPAD(to_char(b.b04),2,'0') || '01','YYYYMMDD'))) = 1

/*
A01 A02_03 A04      B01 B02    B03  B04

no rows selected
*/

drop table a

drop table b