window function count aggregation - sql

Question

I have two quite complex queries going on here. Both should return per given country (Netherlands in this case) the monthly use over the total of 12 months and the percentage that makes up that month of the total of those 12 months.
But the one where i use count as a windowing function returns one more row than the one where i don't use the count as a windowing function.
The query for the left side picture is:
;WITH MonthUsage AS
(
SELECT customer_id, country_name, [Month], [Year], SUM(ItemsPerMonth)
AS ItemsPerMonth
FROM (
SELECT cs.country_name, c.customer_id, YEAR(mol.date_watched) AS Year, MONTH(mol.date_watched) AS [Month], COUNT(*) AS ItemsPerMonth
FROM Customer c
JOIN Customer_Subscription CS ON C.customer_id = CS.customer_id
JOIN Movie_Order_Line mol ON mol.customer_id = c.customer_id
WHERE (mol.date_watched BETWEEN '2017-07-01' AND '2018-07-01') AND cs.country_name = 'Nederland'
GROUP BY c.customer_id,cs.country_name, YEAR(mol.date_watched),
MONTH(mol.date_watched)
UNION ALL
SELECT cs.country_name, c.customer_id, YEAR(sol.date_watched) AS Year,
MONTH(sol.date_watched), COUNT(*) AS ItemsPerMonth
FROM Customer c
JOIN Customer_Subscription CS ON C.customer_id = CS.customer_id
JOIN Show_Order_Line sol ON sol.customer_id = c.customer_id
WHERE sol.date_watched BETWEEN '2017-07-01' AND '2018-07-01'
GROUP BY c.customer_id, cs.country_name, YEAR(sol.date_watched),
MONTH(sol.date_watched)
) AS MonthItems
WHERE country_name = 'Nederland'
GROUP BY customer_id, country_name, [Month], [Year]
),
Months(MonthNumber) AS
(
SELECT 1
UNION ALL
SELECT MonthNumber + 1
FROM months
WHERE MonthNumber < 12
)
SELECT cmb.[Year], ISNULL(cmb.[Month], m.MonthNumber) AS [Month],
ISNULL(ItemsPerMonth, 0) AS ItemsPerMonth,
ISNULL(FORMAT(((CAST(ItemsPerMonth AS decimal) / CAST((
SELECT SUM(ItemsPerMonth)
FROM MonthUsage) AS decimal
))),'P0'), '0%') AS [PercentageOfTotal]
FROM MonthUsage cmb
JOIN Customer c ON c.customer_id = cmb.customer_id
JOIN Months m ON m.MonthNumber = cmb.[Month]
ORDER BY cmb.[Year] ASC, [Month] ASC
And the query for the right picture is:
;WITH MonthUsage AS (
SELECT *
FROM (
SELECT
YEAR(date_watched) AS [Year],
MONTH(date_watched) AS [Month],
COUNT(order_id) OVER(PARTITION BY CONCAT(YEAR(date_watched), MONTH(date_watched))) AS ItemsPerMonth
FROM Movie_Order_Line mov
JOIN Customer c ON c.customer_id = mov.customer_id
JOIN Customer_Subscription cs ON C.customer_id = cs.customer_id
WHERE date_watched BETWEEN '2017-07-01' AND '2018-07-01' AND cs.country_name = 'Nederland'
UNION ALL
SELECT YEAR(date_watched) AS [Year], MONTH(date_watched) AS [Month], COUNT(order_id) OVER(PARTITION BY CONCAT(YEAR(date_watched), MONTH(date_watched))) AS ItemsPerMonth
FROM Show_Order_Line sol
JOIN Customer c ON c.customer_id = sol.customer_id
JOIN Customer_Subscription cs ON C.customer_id = cs.customer_id
WHERE date_watched BETWEEN '2017-07-01' AND '2018-07-01' AND cs.country_name = 'Nederland'
) AS Combined
GROUP BY [YEAR], [Month], ItemsPerMonth
)
SELECT *, ISNULL(FORMAT(((CAST(ItemsPerMonth AS decimal) / CAST((SELECT
SUM(ItemsPerMonth) FROM MonthUsage) AS decimal))),'P0'), '0%') AS
[PercentageOfTotal]
FROM MonthUsage
ORDER BY [Year] ASC, [Month] ASC
I can't seem to figure out why i'm getting different results. Any help is much appreciated. Thank you in advance for your time.