declare @Tb1 table
 (
 ym varchar(7)
 , pri int
 )
 declare @Tb2 table
 (
 ym1 varchar(7)
 ,ym2 varchar(7)
 , rate1 decimal(9,2)
 , rate2 decimal(9,2)
 )
declare @i int
 set @i = 1
 while ( @i < 13) begin
 insert @Tb1(ym , pri )
 values('2013-'+(case when @i < 10 then '0' else '' end)+Convert(Varchar,@i),500000)
 ,('2014-'+(case when @i < 10 then '0' else '' end)+Convert(Varchar,@i ),500000)
 ,('2015-'+(case when @i < 10 then '0' else '' end)+Convert(Varchar,@i ),500000)
 set @i = @i + 1
 
 end
 
 
insert @Tb2
values('2010-01','2010-12','2.4','4.3')
,('2011-01','2011-12','4.1','4.9')
,('2012-01','2012-03','4.5','6.5')
,('2012-04','2013-03','8.9','6.2')
,('2013-04','2014-03','7.4','5.6')
,('2014-01','2015-03','4.5','6.5')

Select * , pri * rate1 as prirate From @Tb1 As t1
 outer Apply
 (
  select top 1 * from
  (
   select top 1 * , 1 as ra from @tb2
   Where ym1 <= t1.ym
   And ym2 >= t1.ym
   union all
   select top 1 * , 2 as ra from @tb2
   Where ym1 < t1.ym or ym2 > t1.ym
   order by ym1 asc
   
  ) as tmp
  order by ra asc
 ) as tt2