Iterate value dynamically - sql

Question

I'm using the below query to calculate a budget value dynamically means iterating upto selected date value.
SUM(case when Name = 'Budget' then Value + ((Value/#TotaldaysinMonth) *
#DaysPastinMonth) end) as [Budget]
Here variable #DaysPastinMonth should be dynamic. Means if I select a date as 03/31/2017. Then the query should run upto the previous month value. Another example is if I select August, then I need to run query from Jan-Aug.
For Jan
SUM(case when Name = 'Budget' then Value + ((Value/#TotaldaysinMonth) *
#DaysPastinJanMonth) end) as [Budget]
For Feb
SUM(case when Name = 'Budget' then Value + ((Value/#TotaldaysinMonth) *
#DaysPastinFebMonth) end) as [Budget]
For Mar
SUM(case when Name = 'Budget' then Value + ((Value/#TotaldaysinMonth) *
#DaysPastinMarMonth) end) as [Budget]
Also I have created variables for all the 12 months which holds DaysPastinMonth.
Can anyone suggest how this can be achieved using case statement.

Answer 1

You are thinking about this in loop when you could do it with set based operations.
----------------------------------------------------------
--Create a table of dates for testing
----------------------------------------------------------
if object_id('tempdb..#dates') is not null
drop table #dates
create table #dates(d date
,RN bigint)
declare #sdate datetime='2017-01-01 00:00'
declare #edate datetime='2017-7-31 00:00'
insert into #dates
select
DATEADD(d,number,#sdate)
,row_number() over (order by (select null)) as RN
from
master..spt_values
where
type='P'
and number<=datediff(d,#sdate,#edate)
declare #numOfDays int = (select count(*) from #dates)
----------------------------------------------------------
--Populate Test Data
----------------------------------------------------------
if object_id('tempdb..#testTable') is not null
drop table #testTable
create table #testTable([Name] varchar(64),
[Value] decimal (16,4),
DT datetime)
insert into #testTable ([Name],[Value],DT)
select
'Budget'
,r.randomNumber
,d.d
from
#dates d
inner join
(SELECT TOP (select #numOfDays)
randomNumber,
row_number() over (order by (select null)) as RN
FROM (
SELECT CAST(ABS(CAST(NEWID() AS binary(6)) %100000) + RAND() AS DECIMAL (16,4)) + 1 randomNumber
FROM sysobjects) sample
GROUP BY randomNumber
ORDER BY randomNumber DESC) r on r.RN = d.RN
union all
select
'Not The Budget'
,r.randomNumber
,d.d
from
#dates d
inner join
(SELECT TOP (select #numOfDays)
randomNumber,
row_number() over (order by (select null)) as RN
FROM (
SELECT CAST(ABS(CAST(NEWID() AS binary(6)) %100000) + RAND() AS DECIMAL (16,4)) + 1 randomNumber
FROM sysobjects) sample
GROUP BY randomNumber
ORDER BY randomNumber DESC) r on r.RN = d.RN
----------------------------------------------------------
--Instead of making your variables "dynamic" which
--would likely consist of some loop, just pass in the
--month you care about and let SQL do the work
----------------------------------------------------------
declare #month datetime = '2016-03-31'
select
DT
,[Value]
,[Name]
,sum(case when [Name] = 'Budget'
then [Value] +
(([Value] / (DATEDIFF(day,DATEADD(month, DATEDIFF(month, 0, #month), 0),#month)))
*
(DATEDIFF(DAY,DATEADD(MONTH, DATEDIFF(MONTH, 0, #month)-1, 0),DATEADD(MONTH, DATEDIFF(MONTH, -1, #month)-1, -1)))) end) as Budget
from
#testTable
where
DT >= DATEADD(yy, DATEDIFF(yy, 0, #month), 0) --this is Jan 1 of the year associated with your vairable
group by
DT
,[Name]
,[Value]