declare @t1 table(期间 int,科目编码 varchar(50),科目名称 varchar(50),c3 money)
declare @t2 table(科目编码 varchar(50),科目名称 varchar(50))

insert into @t1
select 1,'1','科目名称1',100.55 union all
select 1,'2','科目名称2',120.0 union all
select 1,'3','科目名称3',20 union all
select 2,'3','科目名称4',54.21 union all
select 2,'4','科目名称4',5 

insert into @t2
select '1','科目名称1' union all
select '2','科目名称2' union all
select '3','科目名称3' union all
select '4','科目名称4' union all
select '5','科目名称5' 

select * from @t1
select * from @t2
/*
想得到结果:
期间 科目编码    科目名称        c3
1    1    科目名称1    100.55
1    2    科目名称2    120.0
1    3    科目名称3    20
1    4    科目名称4    NULL
1    4    科目名称5    NULL
2    1    科目名称1    NULL
2    2    科目名称2    NULL
2    3    科目名称3    54.21
2    4    科目名称4    5
2    4    科目名称5    NULL

*/

create table t1
(
a int,
b varchar(50),
c varchar(50),
d money
)
insert into t1
select 1,'1','科目名称1',100.55 union all
select 1,'2','科目名称2',120.0 union all
select 1,'3','科目名称3',20 union all
select 2,'4','科目名称4',54.21 union all
select 2,'4','科目名称4',5  
create table t2
(
b varchar(50),
c varchar(50)
)
insert into t2
select '1','科目名称1' union all
select '2','科目名称2' union all
select '3','科目名称3' union all
select '4','科目名称4' union all
select '5','科目名称5'


SELECT t1.a,t3.B,T3.C,t1.d FROM t1  FULL JOIN( SELECT * FROM  t2 ) T3
ON t1.B =T3.b AND t1.c=T3.c

a           B                                                  C                                                  d
----------- -------------------------------------------------- -------------------------------------------------- ---------------------
1           1                                                  科目名称1                                              100.55
1           2                                                  科目名称2                                              120.00
1           3                                                  科目名称3                                              20.00
2           4                                                  科目名称4                                              54.21
2           4                                                  科目名称4                                              5.00
NULL        5                                                  科目名称5                                              NULL

(6 行受影响)