Possible recursive CTE query using date ranges

Question

Not sure how to even phrase the title on this one!

I have the following data:

IF OBJECT_ID (\'tempdb..#data\') IS NOT NULL DROP TABLE #data
CREATE TA         


        

Answer 1

DECLARE @date DATE = GETDATE()

;WITH MonthsCTE AS (
    SELECT 1 [Month], DATEADD(DAY, -DATEPART(DAY, @date)+1, @date) as 'MonthStart'
    UNION ALL
    SELECT [Month] + 1, DATEADD(MONTH, 1, MonthStart)
    FROM MonthsCTE 
    WHERE [Month] < 12 )

SELECT * FROM MonthsCTE

Answer 2

You don't need a "real" recursive CTE here. You can use one for the month references though:

;WITH Months
as
(
    SELECT DATEADD(day, -DATEPART(day, GETDATE())+1, GETDATE()) as 'MonthStart'
    UNION ALL
    SELECT DATEADD(month, -1, MonthStart) as 'MonthStart'
    FROM Months
)

Then you can JOIN to SELECT TOP 13 * FROM Months in your above query.

I'm not going to try to parse all your CASE statements, but essentially you can use a GROUP BY on the date and the MonthStart fields, like:

GROUP BY Datepart(year, monthstart), Datepart(month, monthstart)

and aggregate by month. It will probably be easiest to have all your options (active, lapsed, etc) as columns and calculate each with a SUM(CASE WHEN ... THEN 1 ELSE 0 END) as it will be easier with a GROUP BY.

Answer 3

You can cross join your request with a recursive CTE, this is a good idea.

WITH thirteenMonthBack(myDate, level) as
(
   SELECT GETDATE() as myDate, 0 as level
   UNION ALL
   SELECT DATEADD(month, -1, myDate), level + 1
   FROM thirteenMonthBack
   WHERE level < 13
)
SELECT xxx
FROM youQuery
   CROSS JOIN thirteenMonthBack