Question

So I have a stored procedure that is working except for how it calculates a certain field. On the tables worked with is a field called DeliveryYearMonth that is simply YYYYMM in its format. I try to compare current month info to previous month info, thus I created the following two variables.

DECLARE @CURDate VARCHAR(50) -- Current time (YYYYMM)
DECLARE @MAGDate VARCHAR(50) -- YearAgo Time (YYYYMM)

SET @CURDate = cast((select max(DeliveryYearMonth) from dbo.datatable) as  varchar)
SET @MAGDate = cast((substring(@CURDate,1,4)) as varchar) --For current year
         + cast((substring(@CURDate,5,2) - 1) as varchar) -- To get previous month

This is all fine and dandy unless the the month is January, and thus the month would become 00, and the year would stay the same.

So I tried my hand at an if statement to clear this up.

if(substring(@MAGDate,5,2)) = '00'-- If current Month is January
begin
Set @MAGDate = cast((substring(@CURDate,1,4) - 1) as varchar) --For previous year
         + '12' -- December
end

This always breaks the Month Ago Date (@MAGDate) even if the IF statement isn’t true. I cannot figure out why.

Thanks

Answer 1

To get the previous version of your string, you can do the following:

select replace(convert(varchar(7), dateadd(month, -1, CAST(@CURDate+'01' as DATE)), 121), '-', '')

As a comment suggested, though, you should really just store this as a date, assuming you are using SQL Server 2008 or more recent.