Question

SELECT DATEPART(YEAR, PURCHASE_DATE) AS TRANSACTION_YEAR, DATEPART(MONTH, PURCHASE_DATE) AS TRANSACTION_MONTH,
CASE WHEN DATEPART(YEAR, DUE_DATE) >= DATEPART(YEAR, PURCHASE_DATE) THEN DATEPART(YEAR, DUE_DATE)
ELSE DATEPART(YEAR, PURCHASE_DATE) END AS RELEASE_YEAR, 
CASE WHEN (DATEPART(YEAR, DUE_DATE) = DATEPART(YEAR, PURCHASE_DATE) AND DATEPART(MONTH, DUE_DATE) >= DATEPART(MONTH, PURCHASE_DATE)) THEN DATEPART(MONTH, DUE_DATE)
WHEN DATEPART(YEAR, DUE_DATE) > DATEPART(YEAR, PURCHASE_DATE) THEN DATEPART(MONTH, DUE_DATE)
ELSE
DATEPART(MONTH, PURCHASE_DATE) END AS RELEASE_MONTH,
CAST(YEAR(CASE WHEN DATEPART(YEAR, DUE_DATE) >= DATEPART(YEAR, PURCHASE_DATE) THEN DATEPART(YEAR, DUE_DATE)
ELSE DATEPART(YEAR, PURCHASE_DATE) END) AS VARCHAR(4)) + RIGHT('0'+CAST(MONTH(CASE WHEN (DATEPART(YEAR, DUE_DATE) = DATEPART(YEAR, PURCHASE_DATE) AND DATEPART(MONTH, DUE_DATE) >= DATEPART(MONTH, PURCHASE_DATE)) THEN DATEPART(MONTH, DUE_DATE)
WHEN DATEPART(YEAR, DUE_DATE) > DATEPART(YEAR, PURCHASE_DATE) THEN DATEPART(MONTH, DUE_DATE)
ELSE
DATEPART(MONTH, PURCHASE_DATE) END) AS VARCHAR(2)),2)
FROM TEST

on a sample table of six records generates

2012    1   2012    1   190501
2012    1   2013    12  190501
2011    1   2012    1   190501
2011    1   2011    1   190501
2012    1   2012    1   190501
2012    1   2012    2   190501

What am I doing wrong?

Many thanks!

Answer 1

Why are you trying to do it all in one go and repeating yourself all over the place.

If you start with

select 
DatePart(YEAR,PURCHASE_DATE) as PURCHASE_YEAR,
DatePart(YEAR,DUE_DATE) as DUE_YEAR,
DatePart(MONTH,PURCHASE_DATE) as PURCHASE_MONTH,
DatePart(MONTH,DUE_DATE) as DUE_MONTH
From Test

Then you can do

SELECT PURCHASE_Year AS TRANSACTION_YEAR, 
       PURCHASE_Month) AS TRANSACTION_MONTH,
       CASE 
       WHEN DUE_YEAR >= PURCHASE_YEAR THEN DUE_YEAR
       ELSE PURCHASE_YEAR
       END AS RELEASE_YEAR, 
       CASE 
       WHEN (DUE_YEAR = PURCHASE_YEAR) AND (DUE_MONTH >= PURCHASE_MONTH) THEN DUE_MONTH
       WHEN DUE_YEAR > PURCHASE_YEAR THEN DUE_MONTH
       ELSE PURCHASE_MONTH 
       END AS RELEASE_MONTH,
       CAST(
        CAST(RELEASE_YEAR As VarChar(4)) + 
        '-' + 
        CAST(RELEASE_MONTH as VarChar(2)) + 
        '-1' as DATE) as RELEASE_DATE
FROM (
select 
DatePart(YEAR,PURCHASE_DATE) as PURCHASE_YEAR,
DatePart(YEAR,DUE_DATE) as DUE_YEAR,
DatePart(MONTH,PURCHASE_DATE) as PURCHASE_MONTH,
DatePart(MONTH,DUE_DATE) as DUE_MONTH
From Test
) SomeDummyTableName

I think this is what you were after, and I may even have got it right after wading through that morass.