--> 测试数据：[借出]
go
if object_id('borrow') is not null 
drop table borrow
go
create table borrow(
[borrow_docno] varchar(4),
[borrow_lineno] int,
[borrow_date] datetime,
[borrow_code] varchar(8),
[borrow_qty] int)
insert borrow
select 'A001',10,'2012-1-20','01.01.01',10 union all
select 'A001',20,'2012-1-20','01.01.02',20 union all
select 'A002',30,'2012-2-20','01.01.03',30 union all
select 'A002',20,'2012-2-20','01.01.04',40
--> 测试数据：[还入]
go
if object_id('[return]') is not null 
drop table [return]
go
create table [return](
[back_docno] varchar(4),
[back_line] int,
[back_date] datetime,
[back_code] varchar(8),
[back_qty] int,
[borrow_docno] varchar(4)
)
go
insert [return]
select 'b001',10,'2012-2-20','01.01.01',2,'A001' union all
select 'b002',10,'2012-3-20','01.01.01',3,'A001' union all
select 'b003',10,'2012-3-28','01.01.01',4,'A001' union all
select 'b004',20,'2012-2-10','01.01.02',5,'A001' union all
select 'b005',20,'2012-2-25','01.01.02',1,'A001' union all
select 'b006',20,'2012-3-25','01.01.02',1,'A001' union all
select 'b007',20,'2012-3-26','01.01.02',1,'A001'


select back_line,convert(varchar(10),MAX(back_date),120) as back_date,
back_code,sum(back_qty) as back_qty,
borrow_docno from [return] b group by back_line,month(back_date),
back_code,borrow_docno

/*
back_line    back_date    back_code    back_qty    borrow_docno
10    2012-02-20    01.01.01    2    A001
10    2012-03-28    01.01.01    7    A001
20    2012-02-25    01.01.02    6    A001
20    2012-03-26    01.01.02    2    A001
*/