select PCode, Currency 
    ,Rate=(select top 1 Rate from A where Code=B.Code and StartDate<EnabledDate order by StartDate desc)
    ,PriceRMB=(select top 1 Rate from A where Code=B.Code and StartDate<EnabledDate order by StartDate desc)*Price
    ,EnabledDate 
from B

------解决方案--------------------
写法就是这样,随手敲的,不排除手误.
当然,也可以用临时表按startdate和enabledate分别生成identity列,然后用identity列去连表
SQL code
select b.pcode,b.currency,a.rate,b.price*a.rate priceRMB,b.enabledDate
   from tB b
inner join tA a
   on
   (select count(*) from tB x where x.EnabledDate<b.EnabledDate)
   =
   (select count(*) from tA x where x.StartDate<a.StartDate)

------解决方案--------------------
SQL code

select id= identity(int,1,1),* into #tb1 from ta
select id= identity(int,1,1),* into #tb2 from tb
select b. pcode,b.currency,a.rate,pricermb=(a.rate*b.price),b.enabledate from #tb1 a on #tb2 b on a.code=b.currency

------解决方案--------------------


select B.PCode ,B.Currency,A.Rate ,(A.Rate*B.Price)as PriceRMB,B.EnabledDate from A,B
where A.Currency=B.Currency