Sum of previous rows and multiply with value from another column

Question

I have a table with around 80000 records. Here is an example:

startyear	division	account	budget	forecast
2021	40	4100	5122952,22	0,012306656
2022	40	4100	0	0,011424198
2023	40	4100	0	0,010431491
2024	40	4100	0	0,009311863
2025	40	4100	0	0,008324122
2026	40	4100	0	0,007763793
2027	40	4100	0	0,007557735
2028	40	4100	0	0,007357883
2029	40	4100	0	0,007160051
2030	40	4100	0	0,006953345
2031	40	4100	0	0,006737952
2032	40	4100	0	0,006535297
2033	40	4100	0	0,006364179
2034	40	4100	0	0,006213237
2035	40	4100	0	0,006085724
2036	40	4100	0	0,005944279
2037	40	4100	0	0,005758285
2038	40	4100	0	0,005559474
2039	40	4100	0	0,005360105
2040	40	4100	0	0,005163794
2041	40	4100	0	0,004972228

I'm trying to calculate a new column starting with the budget from line 1. So year 2021 will be the same. the first calculation is correct. But the rest of the calculation ignores the changes before. This is the code:

WITH cte AS (
SELECT startyear, division, account, forecast, SUM(budget) AS asum
FROM @table
GROUP BY startyear,
         division,
         account,
         forecast
), cteRanked AS (
SELECT cte.startyear,
             cte.division,
             cte.account,
             cte.forecast,
             cte.asum AS asum
FROM cte
)
SELECT c1.startyear,
          c1.division,
          c1.account,
          c1.forecast,
          c1.asum , ISNULL((SELECT SUM(c2.asum)*c1.forecast 
FROM cteRanked c2 
WHERE c1.startyear > 2021 
    AND c2.startyear < c1.startyear 
    AND c2.division = c1.division 
    AND c2.account = c1.account), c1.asum) AS Bud
FROM cteRanked c1
ORDER BY c1.division, c1.account, c1.startyear

Gives this result:

startyear	division	account	forecast	budget	result	correct
2021	40	4100	0,012306656	5122952,22	5122952,22	5122952,22
2022	40	4100	0,011424198	0	58525,62051	58525,62
2023	40	4100	0,010431491	0	53440,02998	54050,54
2024	40	4100	0,009311863	0	47704,22923	48752,52
2025	40	4100	0,008324122	0	42644,07928	43987,00
2026	40	4100	0,007763793	0	39773,54059	41367,57

As you can see this query does not cumulate the results when the query runs. Anyone have any ideas?

Answer 1

While your post is lacking some vital information...I don't necessarily blame you because it's a difficult problem to both explain and to solve.

It looks like you're basically trying to come up with a compounding interest calculator. Except in this case, the rate changes every year.

To calculate the PRODUCT aggregate of your forecasts, I found this blog post: https://blog.jooq.org/2018/09/21/how-to-write-a-multiplication-aggregate-function-in-sql/

It just required a very tiny bit of tweaking.

This is my answer:

DECLARE @StartingYear int = 2021,
        @StartingBudget decimal(12, 2);

SELECT @StartingBudget = yt.budget
FROM #YourTable yt
WHERE yt.startyear = @StartingYear

SELECT yt.startyear, yt.division, yt.account, yt.budget, yt.forecast, YearBudget = yt.budget, PrevYearDiff = yt.budget
FROM #YourTable yt
WHERE yt.startyear = @StartingYear
UNION ALL
SELECT x.startyear, x.division, x.account, x.budget, x.forecast
     , YearBudget = CONVERT(decimal(10,2), x.SumProdBudget)
     , PrevYearDiff = CONVERT(decimal(10,2), x.SumProdBudget - LAG(x.SumProdBudget,1,@StartingBudget) OVER (ORDER BY x.startyear))
FROM (
    SELECT yt.startyear, yt.division, yt.account, yt.budget, yt.forecast
        , SumProdBudget = EXP(SUM(LOG(1+yt.forecast)) OVER (ORDER BY yt.startyear)) * @StartingBudget
    FROM #YourTable yt
    WHERE yt.startyear > @StartingYear
) x

Returns:

| startyear | division | account | budget     | forecast    | YearBudget | PrevYearDiff | 
|-----------|----------|---------|------------|-------------|------------|--------------| 
| 2021      | 40       | 4100    | 5122952.22 | 0.012306656 | 5122952.22 | 5122952.22   | 
| 2022      | 40       | 4100    | 0.00       | 0.011424198 | 5181477.84 | 58525.62     | 
| 2023      | 40       | 4100    | 0.00       | 0.010431491 | 5235528.38 | 54050.54     | 
| 2024      | 40       | 4100    | 0.00       | 0.009311863 | 5284280.90 | 48752.52     | 
| 2025      | 40       | 4100    | 0.00       | 0.008324122 | 5328267.90 | 43987.00     | 
| 2026      | 40       | 4100    | 0.00       | 0.007763793 | 5369635.47 | 41367.57     | 

The key to this whole thing is this line:

SELECT SumProdBudget = EXP(SUM(LOG(1+yt.forecast)) OVER (ORDER BY yt.startyear)) * @StartingBudget

This is saying to return a running product of all previous forecasts, then multiply that by the original budget. This will produce the budget for each year, technically based on the budget of the previous year.

Then once you have that, I stuck it in a sub-query to find the difference between the year and its previous year.

---

Sample Data:

IF OBJECT_ID('tempdb..#YourTable','U') IS NOT NULL DROP TABLE #YourTable; --SELECT * FROM #YourTable
CREATE TABLE #YourTable (
    startyear   int             NOT NULL,
    division    int             NOT NULL,
    account     int             NOT NULL,
    budget      decimal(12, 2)  NOT NULL,
    forecast    decimal(10, 9)  NOT NULL,
);

INSERT INTO #YourTable (startyear, division, account, budget, forecast)
VALUES (2021, 40, 4100, 5122952.22, 0.012306656)
     , (2022, 40, 4100, 0         , 0.011424198)
     , (2023, 40, 4100, 0         , 0.010431491)
     , (2024, 40, 4100, 0         , 0.009311863)
     , (2025, 40, 4100, 0         , 0.008324122)
     , (2026, 40, 4100, 0         , 0.007763793)
     , (2027, 40, 4100, 0         , 0.007557735)
     , (2028, 40, 4100, 0         , 0.007357883)
     , (2029, 40, 4100, 0         , 0.007160051)
     , (2030, 40, 4100, 0         , 0.006953345)
     , (2031, 40, 4100, 0         , 0.006737952)
     , (2032, 40, 4100, 0         , 0.006535297)
     , (2033, 40, 4100, 0         , 0.006364179)
     , (2034, 40, 4100, 0         , 0.006213237)
     , (2035, 40, 4100, 0         , 0.006085724)
     , (2036, 40, 4100, 0         , 0.005944279)
     , (2037, 40, 4100, 0         , 0.005758285)
     , (2038, 40, 4100, 0         , 0.005559474)
     , (2039, 40, 4100, 0         , 0.005360105)
     , (2040, 40, 4100, 0         , 0.005163794)
     , (2041, 40, 4100, 0         , 0.004972228);