Cumulative Summation in SQL Server - sql

Question

I'm writing a query, part of Stored Procedure in SQL Server. I need to find cumulative summation in SQL Server.
A variable will hold a integer value say 100. Let's say
Declare #Variable int = 100
Now the #NewVariable will have below formula:
#NewVariable = #Variable * (1 - 0.005)
Hence #NewVariable = 99.5
Now, the #NewestVariable will have below formula;
#NewestVariable = #NewVariable * (1 - 0.005)
Hence the #NewestVariable will have value of 99.00
Likewise this calculation will occur 24 times and all the results will be sum at the end.
Hence final result will be: 100 + 99.5 +99.00 + .... ...
I tried to achieve the desired result using #Count Variable (DECLARE #COUNT INT = 24) and using a While loop, but I'm not sure whether I'm correct or not?
Request your help!
Thanks!

Answer 1

You can do it using a CTE as below:
declare #variable int = 100
;with cte as
(
select convert(numeric(8,2), #variable) as var, 1 as recCount
union all
select convert(numeric(8,2), #variable * (1 - recCount*0.005)) as var, recCount+1 as recCount
from cte
where recCount < 24
)
select sum(var) as total from cte
Working Fiddle Demo
Edit: Adjusted to resolve rounding error as per #peter.petrov 's comment
If you need to get the values of each row before counting, please use this fiddle

Answer 2

Try this code.
declare #Variable decimal(20,10);
set #Variable = 100;
declare #Sum decimal(20,10);
set #Sum = 0;
declare #cnt int;
set #cnt = 1;
while (#cnt <= 24)
begin
set #Sum = #Sum + #Variable;
set #Variable = #Variable * (1.0 - 0.005);
set #cnt = #cnt + 1;
end;
select #Sum;

Answer 3

A simple answer would be like this
DECLARE #Variable INT = 100
SELECT #Variable
DECLARE #counter INT = 1
DECLARE #SumVariable NUMERIC(20,2) = #Variable
DECLARE #NewVariable NUMERIC(20,2) = #Variable
WHILE(#counter<24)
BEGIN
SET #NewVariable = #NewVariable * 0.995
SET #SumVariable = #SumVariable + #NewVariable
SET #counter = #counter+1
END
SELECT #SumVariable

Answer 4

You could also use a "quirky update" to avoid while-loops. If you're not interesed in intermediate resuls, just modify the last code line to select only the max(total).
DECLARE #total DECIMAL(10,3) = 0.000
;WITH "data" AS
(
SELECT CAST( 100 AS DECIMAL(10,3)) AS id
UNION ALL
SELECT CAST( id * ( 1 - 0.005 ) AS DECIMAL(10,3)) FROM "data" WHERE id > 100 * (1 - 21 * 0.005)
)
SELECT
id, total = CAST( 0.000 AS DECIMAL(10,3))
INTO #temp
FROM
"data"
OPTION ( MAXRECURSION 23 );
UPDATE t SET #total = total = #total + id FROM #temp t
SELECT * FROM #temp
See SQL-Fiddle for testing.