Get total sales of last 12 months even if values are null - sql

Question

I have following code in which it presently gives month wise Total Sales for current year, I need to get total sales from last month of previous year to current month of this year.
My query is as follows:
;WITH mcte AS (
SELECT DATEADD(year, -1, getdate()) as MONTH_NAME
UNION ALL
SELECT DATEADD(MONTH,1,MONTH_NAME)
FROM mcte
WHERE DATEPART(MONTH,MONTH_NAME) < 12),octe AS(
SELECT (DATENAME (MONTH, DATEADD ( MONTH, DATEPART(MONTH, OI.CreatedDate), -1) )) AS MONTH_NAME,
SUM (OI.ItemQty * OI.TotalPrice) AS TOTAL_SALES
FROM Order_Item OI
GROUP BY MONTH(OI.CreatedDate))
SELECT DATENAME(MONTH,m.MONTH_NAME) + '' + DATENAME(YEAR,m.MONTH_NAME) as
MONTH_NAME, o.TOTAL_SALES FROM mcte m LEFT JOIN octe o ON o.MONTH_NAME = DATENAME(MONTH,m.MONTH_NAME)
and I am getting records
MONTH_NAME TOTAL_SALES
July2019 54023.45
August2019 NULL
December2019 NULL
September2019 NULL
October2019 NULL
November2019 NULL
Here I am only getting data for previous year only, not getting data for current year.Can anyone please guide me on this.
Thank you

Answer 1

You are only generating months up to 12. Try replacing the first CTE with:
WITH mcte AS (
SELECT DATEADD(year, -1, getdate()) as MONTH_NAME
UNION ALL
SELECT DATEADD(MONTH,1,MONTH_NAME)
FROM mcte
WHERE month_name < GETDATE()
),
Note the difference is the WHERE clause.
The entire query should look like this:
WITH months AS (
SELECT DATEFROMPARTS(YEAR(getdate()) - 1, MONTH(getdate()), 1) as month
UNION ALL
SELECT DATEADD(MONTH, 1, month)
FROM months
WHERE EOMONTH(month) < GETDATE()
)
SELECT m.month, SUM(OI.ItemQty * OI.TotalPrice) AS TOTAL_SALES
FROM months m LEFT JOIN
Order_Item OI oi
ON oi.CreatedDate >= m.month AND
oi.CreatedDate < DATEAADD(month, 1, m.month)
GROUP BY m.month

Answer 2

Try doing this:
DECLARE #CurDate DATE = GET_DATE()
DECLARE #OneYearPrior DATE = DATEADD(YEAR, -1, #CurDate)
WITH relevant_months(start_date, month_of_sale, year_of_sale) AS (
SELECT
#CurDate AS start_date,
MONTH(#CurDate) as month_of_sale,
YEAR(#CurDate) as year_of_sale
UNION ALL
SELECT DATEADD(MONTH, -1, start_date) AS start_date,
MONTH(DATEADD(MONTH, -1, start_date)) as month_of_sale,
YEAR(DATEADD(MONTH, -1, start_date)) AS year_of_sale
FROM relevant_months
WHERE DATEADD(MONTH, -1, start_date) >= #OneYearPrior
),
relevant_data AS (
SELECT OI.CreatedDate,
OI.ItemQty,
OI.TotalPrice,
MONTH(OI.CreatedDate), AS month_of_sale,
YEAR(OI.CreatedDate) AS year_of_sale
FROM Order_Item OI
WHERE OI.CreatedDate >= DATEADD(YEAR, -1, GETDATE())
)
SELECT rm.month_of_sale as month, rm.year_of_sale as year,
SUM(rd.ItemQty*rd.TotalPrice) as total_sales
FROM relevant_months rm
LEFT JOIN relevant_data rd
ON rm.month_of_sale = rd.month_of_sale
AND rm.year_of_sale = rd.year_of_sale
GROUP BY rm.month_of_sale, rm.year_of_sale
ORDER BY rm.year_of_sale asc, rm.month_of_sale asc