with a as 

(

select product_name,weight,ftbl where 月份 = 12

)

,b as

(

select product_name,月份,max(weight) weight  from 表 where 月份 < 12 group by product_name, 月份 

)

select b.product_name,b.weight,a.ftbl,b.weight*a.ftbl from b inner join a on b.product_name = a.product_name union all

select product_name,weight,ftbl,weight*ftbl from a

之前月份的加上12-月的数字。。。后强行把月份弄成一列都是12月。然后匹配12月的比例就行了

比如11月假如你存的是   11数字        多一列出来就让它变成12，然后用多的这一列子查询12月的就行

类似这样？

select 

t1.month_num,

t1.number_total,

t1.number_total*t2.bl1 as zl1,

t1.number_total*t2.bl2 as zl2

from

(

select 11 as month_num,30 as number_total,11+(12-11) as December

union all

select 10 as month_num,50 as number_total,10+(12-10) as December) t1

join 

(select 12 as month_num,1000 as number_total,0.45 as bl1, 0.92 as bl2 ) t2

on t1.December=t2.month_num

等等。在修改