Fix for statistics pipline to display proper last 6 weeks data around the new year

src/Stats.Warehouse/Programmability/Stored Procedures/dbo.DownloadReportLast6Weeks.sql

@@ -19,31 +19,39 @@ BEGIN
 		AND	[Year] = @MinYear
 
 	DECLARE @Cursor DATETIME = (SELECT ISNULL(MAX([Position]), @ReportGenerationTime) FROM [dbo].[Cursors] (NOLOCK) WHERE [Name] = 'GetDirtyPackageId')
-
-	SELECT	TOP 6 D.[Year],
+	DECLARE @MaxDate DATE = DATEADD(DAY, 42, @MinDate);
+
+	WITH WeekLookup AS 
+	(
+		-- If we just take all the rows between @MinDate and @MaxDate from Dimension_Date table
+		-- we might end up the days from the week that contains 1st of January to have two
+		-- different week numbers:
+		-- 12/30/2018 -> 53rd of 2018
+		-- 12/31/2018 -> 53rd of 2018
+		-- 1/1/2019 -> 1st of 2019
+		-- 1/2/2019 -> 1st of 2019
+		-- etc.
+		-- which results in the wrong grouping when group by [WeekOfYear] and [Year] is done:
+		-- the single week gets split into two portions, one for the previous year and another for
+		-- the new one with aggregations calculated separately for each of the portions.
+		-- This CTE works around the issue by making sure that all days of the week map to
+		-- the same [WeekOfYear] and [Year], specifically to that of the first day of that week.
+		SELECT d.[Id], dd.[WeekOfYear], dd.[Year]
+		FROM [dbo].[Dimension_Date] AS d WITH(NOLOCK)
+		CROSS APPLY
+		(
+			SELECT TOP(1) [WeekOfYear], [Year]
+			FROM [dbo].[Dimension_Date] AS d2 WITH(NOLOCK)
+			WHERE d2.[Date] <= d.[Date] AND d2.[DayOfWeek] = 1
+			ORDER BY d2.[Date] DESC
+		) AS dd
+		WHERE d.[Date] >= @MinDate AND d.[Date] < @MaxDate AND d.[Date] <= @Cursor
+	)
+	SELECT	D.[Year],
 			D.[WeekOfYear],
-			SUM(ISNULL(Facts.[DownloadCount], 0)) 'Downloads'
+			SUM(ISNULL(Facts.[DownloadCount], 0)) AS [Downloads]
 	FROM	[dbo].[Fact_Download] AS Facts (NOLOCK)
-
-	INNER JOIN	[dbo].[Dimension_Date] AS D (NOLOCK)
-	ON			D.[Id] = Facts.[Dimension_Date_Id]
-
-	WHERE	D.[Date] IS NOT NULL
-			AND ISNULL(D.[Date], CONVERT(DATE, '1900-01-01')) >=
-				DATETIMEFROMPARTS(
-					DATEPART(year, @MinDate),
-					DATEPART(month, @MinDate),
-					DATEPART(day, @MinDate),
-					0, 0, 0, 0)
-			AND ISNULL(D.[Date], CONVERT(DATE, DATEADD(day, 1, @ReportGenerationTime))) <
-				DATETIMEFROMPARTS(
-					DATEPART(year, @ReportGenerationTime),
-					DATEPART(month, @ReportGenerationTime),
-					DATEPART(day, @ReportGenerationTime),
-					0, 0, 0, 0)
-			AND Facts.[Timestamp] <= @Cursor
-
-	GROUP BY	D.[Year], D.[WeekOfYear]
-	ORDER BY	[Year], [WeekOfYear]
-
+	INNER JOIN WeekLookup AS D ON D.Id = Facts.Dimension_Date_Id
+	GROUP BY D.[Year], D.[WeekOfYear]
+	ORDER BY [Year], [WeekOfYear]
 END