How to calculate Running Multiplication

Question

I have two tables

WAC table

ID  wac_inc             item
--  -----------------   ----
1   2.310000000000000   A
2   1.10000000000000         


        

Answer 1

you could do it easily with a recursive cte:

with rec(id ,wi,i,r) as 
(
  select top (1) w.ID,w.wac_inc,w.item, b.baseline * (1 + (w.wac_inc/100))
  from wac w join baseline b on w.item=b.item
  union all
  select w.ID,w.wac_inc,w.item, r.r * (1 + (w.wac_inc/100))
  from wac w
  join rec r on (w.ID)-1 = r.id
 )
 select * from rec

Output:

1   2.31    A   10.231
2   1.1     A   10.343541
3   2.13    A   10.563858
4   1.34    A   10.705414

check in the demo

---

EDIT - Adding another solution:

you can do it by taking help from a copy of your original table :

Assuming your schema and data is:

create  table wac
  (ID int,wac_inc numeric(38,15),item char )

insert wac
values (1,2.31,'A'),
(2,1.1,'A'),
(3,2.13,'A'),
(4,1.34,'A')

1.take a copy from original table(use a temp table or a table variable) and update the first record from baseline table:

create table  #tmp (ID int,wac_inc numeric(38,15),item char, Running_Mul numeric(38,15))
insert into #tmp select id,wac_inc,item,null from wac

update #tmp set Running_Mul = (select top 1 baseline from baseline)*(1+(wac_inc/100))
where id = (select min(id) from #tmp)

2.declare these variables:

declare @id int,@rm numeric(38,15)
select @id=min(id) from #tmp

select @rm=Running_Mul from #tmp where id=@id

3.update the copy:

update #tmp
set @rm=Running_Mul= case 
                    when @id <> id then @rm*(1+(wac_inc/100))
                    else Running_Mul
                 end,
@id=id

and now you can check the result:

select * from #tmp
drop table #tmp

Result:

ID  wac_inc             item    Running_Mul
1   2.310000000000000   A   10.231000000000000
2   1.100000000000000   A   10.343541000000000
3   2.130000000000000   A   10.563858000000000
4   1.340000000000000   A   10.705414000000000