If/Then/Else in Formatting a Date - sql

Question

I am trying to get the fiscal period and year out of an invoice date. Using the month() function together with the Case I am able to get the period. since Period 1 is in November I need to do a +1 1 the year when this is true
Using the IF function together with the date functions are now working for me.
My query is
Select a.OrderAccount
,a.InvoiceAccount
,a.InvoiceDate
,year(a.InvoiceDate) as Year
,month(a.InvoiceDate) as Month,
Case month(a.InvoiceDate)
WHEN '11' THEN '1' -- increase year by +1
WHEN '12' THEN '2'-- increase year by +1
WHEN '1' THEN '3'
WHEN '2' THEN '4'
WHEN '3' THEN '5'
Any advice would be appreciated. Thanks

Answer 1

Use DATEADD to just add 2 months to the original date:
MONTH(DATEADD(month,2,a.InvoiceDate)) as FiscalMonth,
YEAR(DATEADD(month,2,a.InvoiceDate)) AS FiscalYear,

Answer 2

Create and populate a Calendar Table (it makes working with dates much easier).
create table Calendar
(
id int primary key identity,
[date] datetime,
[day] as datepart(day, [date]) persisted,
[month] as datepart(month, [date]) persisted,
[year] as datepart(year, [date]) persisted,
day_of_year as datepart(dayofyear, [date]) persisted,
[week] as datepart(week, [date]),
day_name as datename(dw, [date]),
is_weekend as case when datepart(dw, [date]) = 7 or datepart(dw, [date]) = 1 then 1 else 0 end,
[quarter] as datepart(quarter, [date]) persisted
--etc...
)
--populate the calendar
declare #date datetime
set #date = '1-1-2000'
while #date <= '12-31-2100'
begin
insert Calendar select #date
set #date = dateadd(day, 1, #date)
end
Then, create a FiscalYear view:
create view FiscalYear
as
select
id,
case when month = 11 or month = 12 then year + 1 else year end as [year]
from Calendar
So, whenever you need the fiscal year of a given date, just use something like the following query:
select C.*, FY.year fiscal_year from Calendar C inner join FiscalYear FY on FY.id = C.id
Of course, since fiscal year is just a computation on a column, you could also just make it a part of the calendar table itself. Then, it's simply:
select * from Calendar

Answer 3

If you want to stick with arithmetic: The fiscal month is ( Month( a.InvoiceDate ) + 1 ) % 12 + 1 and the value to add to the calendar year to get the fiscal year is Month( a.InvoiceDate ) / 11.
The following code demonstrates 12 months:
with Months as (
select 1 as M
union all
select M + 1
from Months
where M < 12 )
select M, ( M + 1 ) % 12 + 1 as FM, M / 11 as FYOffset
from Months;
D Stanley's answer makes your intention clearer, always a consideration for maintainability.

Answer 4

If you have this logic in 10 different places and the logic changes starting (say) on 1/1/2018 you will have a mess on your hands.
Create a function that has the logic and then use the function like:
SELECT InvoiceDate, dbo.FiscalPeriod(InvoiceDate) AS FP
FROM ...
Something like:
CREATE FUNCTION dbo.FiscalPeriod(#InvoiceDate DateTime)
RETURNS int
AS BEGIN
DECLARE #FiscalDate DateTime
SET #FiscalDate = DATEADD(month, 2, #InvoiceDate)
RETURN YEAR(#FiscalDate) * 100 + MONTH(#FiscalDate)
END
This returns values like 201705, but you could have dbo.FiscalPeriodMonth() and dbo.FiscalPeriodYear() if you needed. And you can have as complicated logic as you need in one place.