declare @A表 table 
(id int,size1 int,size2 int,size3 int,size4 int,size5 int)
insert into @A表
select 1,0,0,0,1,0 union all
select 2,1,1,0,1,0

declare @B表 table (id int,qty1 int,qty2 int,qty3 int,qty4 int,qty5 int)
insert into @B表
select 1,0,0,0,1,0 union all
select 2,1,1,1,1,0

SELECT  有效值 = a.size1 * b.qty1 + a.size2 * b.qty2 + a.size3 * b.qty3 + a.size4
        * b.qty4 + a.size5 * b.qty5
FROM    @A表 a
        LEFT JOIN @B表 b ON a.id = b.id
/*
有效值
-----------
1
3
*/

------解决方案--------------------
如果值是固定0和1时可以去掉sign,如果是>=0时要加上

------解决方案--------------------
如果没有NULL值,并且都大于等于零,则直接

SELECT  
size1*qty1+size2*qty2+size3*qty3+size4*qty4+size5*qty5
FROM A,B where 连接条件

如果有NULL值,或者相乘的结果可能小于零,且要丢弃,则要判断:

SELECT  
(case when size1*qty1>0 then size1*qty2 else 0 end)+
(case when size2*qty2>0 then size2*qty2 else 0 end)+
(case when size3*qty3>0 then size3*qty3 else 0 end)+
(case when size4*qty4>0 then size4*qty4 else 0 end)+
(case when size5*qty5>0 then size5*qty5 else 0 end)
FROM A,B where 连接条件