Вам, вероятно, нужна таблица календаря. Вот быстрый способ его создания с непроверенной реализацией вашего кода. Я предполагаю, что StartDate может содержать компонент времени, поэтому необходимо объединить даты.
DECLARE @StartYear DATETIME = '20200101'
DECLARE @days INT = 366
;WITH
E1(N) AS (
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
), -- 1*10^1 or 10 rows
E2(N) AS (SELECT 1 FROM E1 a, E1 b), -- 1*10^2 or 100 rows
E4(N) AS (SELECT 1 FROM E2 a, E2 b), -- 1*10^4 or 10,000 rows
E8(N) AS (SELECT 1 FROM E4 a, E4 b), -- 1*10^8 or 100,000,000 rows
Tally(N) AS (SELECT TOP (@Days) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E8),
Calendar AS (
SELECT StartOfDay = DATEADD(dd,N-1,@StartYear),
EndOfDay = DATEADD(second, -1, DATEADD(dd,N ,@StartYear))
FROM Tally)
SELECT DATEADD (week, datediff(week, 0, COALESCE(x.StartDate, c.StartOfDay) ), -1) as 'WeekOf'
, DATEADD (week, datediff(week, 0, COALESCE(x.StartDate, c.StartOfDay)), +5) as 'to'
, DATEPART(wk, COALESCE(x.StartDate, c.StartOfDay)) as 'WeekNumber'
FROM Calendar c
INNER JOIN [DESOutage].[dbo].[OPSInterruption] x
ON x.StartDate > c.StartOfDay AND x.StartDate <= c.EndOfDay
WHERE c.StartOfDay > '2020-01-01' AND c.StartOfDay <'2020-02-01'
GROUP BY DATEADD (week, datediff(week, 0, COALESCE(x.StartDate, c.StartOfDay)), -1),
DATEPART(wk, COALESCE(x.StartDate, c.StartOfDay)),
DATEADD (week, datediff(week, 0, COALESCE(x.StartDate, c.StartOfDay)), +5)