DECLARE @YEAR INT, @MONTH INT
SELECT @YEAR = 2005, @MONTH = 6

DECLARE @StartDate DATETIME, @EndDate DATETIME
SET @StartDate = CONVERT(DATETIME,CAST(@YEAR AS CHAR(4))+RIGHT('0'+CAST(@MONTH AS VARCHAR(2)),2)+'01',112)
SET @EndDate = DATEADD(mm,13,@StartDate)
SELECT @StartDate, @EndDate -- eyeball

SELECT 
	c.Reference, 
	mc.MPAN--,
	--ElementID,
	--mm = MONTH(hhdatetime),
	--yy = YEAR(hhdatetime) 
FROM CONTRACTS.MPAN_Contract mc
join CONTRACTS.ContractElementUnitInstance ui
	on mc.ContractID = ui.ContractID
join CONTRACTS.Contract c 
	on ui.ContractID = c.id
	and ui.ElementID in (2,3,4)
join CONTRACTS.CalendarAllHH cal
	on cal.HHDatetime between ui.Startdate and ui.Enddate
	and cal.HHDatetime between mc.startdate and mc.enddate
	
WHERE cal.HHDatetime >= @StartDate AND cal.HHDatetime < @EndDate

GROUP BY c.Reference, mc.MPAN, ElementID, MONTH(hhdatetime), YEAR(hhdatetime)

create view dbo.withClusteredIdx
with schemabinding
as
select c.Reference, mc.MPAN,ElementID,MONTH(hhdatetime) mm,YEAR(hhdatetime) yy
...
group by YEAR(hhdatetime),MONTH(hhdatetime),c.Reference, mc.MPAN,ElementID


CREATE UNIQUE CLUSTERED INDEX [idxTest] ON [dbo].[withClusteredIdx] 
(
[yy] ASC,
[mm] ASC,
[Reference] ASC,
[MPAN] ASC,
[ElementID] ASC
)
go


SELECT ...
FROM dbo.withClusteredIdx
WHERE
    yy >= @YEAR ... AND
    mm ...

DATEADD(mm, DATEDIFF(mm, 0, hhdatetime), 0) MonthOfYear