Create Calculated Value On Same Calculated Value Inside Previous Row

Question

I'm trying to make a script to calculate "SHI" Column using SQL based on this table.

| Day | BR  | BR2 | HI  |  SHI   |
----------------------------------
|  1  | 0   |  0  | 0   |  0     |
|  2  | 400 | 400 | 95  |  95    |
|  3  | 0   | 400 | 0   |  95    |
|  4  | 350 | 750 | 100 |  97.33 |
|  5  | 350 |1100 | 100 |  98.18 |

I need to calculate the SHI Column using:

SHI  =  ((BR * HI) + (Prev.SHI * Prev.BR2)) / BR2

Just to be clear, the SHI Column do not exist in my data yet. That is what I am trying to have my query calculate. My problem is, I don't know how to get the previous SHI Value to insert on that formula for current day.

Any idea how to create this in SQL?

Answer 1

With cte you can achieve your desired result.

with cte as 
(
select day,br,br2,hi,(case when br2<>0 and br2 is not null then coalesce(round( ((br*hi))/br2,2),0) else 0 end)SHI from S66312677V2 where day=1
union all 
select s.day,s.br,s.br2,s.hi,
(case when s.br2<>0 and s.br2 is not null then coalesce(round( ((s.br*s.hi)+cte.shi*cte.br2)/s.br2,2),0) else 0 end)SHI from S66312677V2 s
inner join cte on s.day-1=cte.day
where s.day<>1
)
select * from cte

Output:

If number of rows is more than 100 then use OPTION (MAXRECURSION xxx) to set a larger recursion limit up-to 32,767 as below:

    with cte as 
        (
        select day,br,br2,hi,(case when br2<>0 and br2 is not null then coalesce(round( ((br*hi))/br2,2),0) else 0 end)SHI from S66312677V2 where day=1
        union all 
        select s.day,s.br,s.br2,s.hi,
        (case when s.br2<>0 and s.br2 is not null then coalesce(round( ((s.br*s.hi)+cte.shi*cte.br2)/s.br2,2),0) else 0 end)SHI from S66312677V2 s
        inner join cte on s.day-1=cte.day
        where s.day<>1
        )
        select * from cte
OPTION (MAXRECURSION 999)