SQL Server中的累积求和

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.