在线求一个SQL语句，大家帮帮忙，先谢了

[sqllong]

表1
bookid bookcount
------------------------------ -----------
ISBN号 10
测试2 5
ISBN号 7

表2
bookid bookcount
------------------------------ -----------
ISBN号 1
ISBN号 1
ISBN号 2
ISBN号 1
ISBN号 1

我期望结果
表1中bookid所有的数量 减去 表2中对应的bookid所有的数量（可能在表2中没有表1中出现的bookid） 得到如下结果：

bookid bookcount
------------------------------ -----------
ISBN号 11
测试2 5

在线等，大家帮帮忙，谢谢咯

[xeqtr1982]

declare @t table(bookid varchar(10),bookcount int)
insert into @t select 'ISBN号',10
union all select '测试2',5
union all select 'ISBN号',7

declare @a table(bookid varchar(10),bookcount int)
insert into @a select 'ISBN号',1
union all select 'ISBN号',1
union all select 'ISBN号',2
union all select 'ISBN号',1
union all select 'ISBN号',1



select a.bookid,isnull(a.bookcount,0)-isnull(b.bookcount,0) as bookcount from (select bookid,sum(bookcount) as bookcount from @t group by bookid)a,(select bookid,sum(bookcount) as bookcount from @a group by bookid)b where a.bookid*=b.bookid

[xeqtr1982]

declare @t table(bookid varchar(10),bookcount int)
insert into @t select 'ISBN号',10
union all select '测试2',5
union all select 'ISBN号',7

declare @a table(bookid varchar(10),bookcount int)
insert into @a select 'ISBN号',1
union all select 'ISBN号',1
union all select 'ISBN号',2
union all select 'ISBN号',1
union all select 'ISBN号',1

select a.bookid,sum(a.bookcount) as bookcount
from
(
select bookid,bookcount from @t
union all
select bookid,-1*bookcount from @a
)a
group by a.bookid

[sqllong]

谢谢了

[sqllong]

where a.bookid*=b.bookid 那个* 是什么意思呢
请教下