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Indexed Views - why don't they improve performance?!!!!


Indexed Views - why don't they improve performance?!!!!

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ChrisM@Work
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Have you tried figuring out the filters and applying to the inner query? Something like this:

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)



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Gazareth
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ChrisM@Work (1/23/2013)
Have you tried figuring out the filters and applying to the inner query? Something like this:

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)



I did wonder if the view was created to allow direct use of the @Month & @Year parameters.
I also assume the group by clause is there to remove duplicates - any ideas on if that or distinct performs better?
Grant Fritchey
Grant Fritchey
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Can't see the plan. I'm getting encoding errors. If you save the plan as a .sqlplan file, you can attach it. Then it can be downloaded.

Just on what I can see though, it looks like it's expanding the view. For giggles, try the noexpand hint when you create the indexed view. Since the query is clearly going to lead to scans (functions on the GROUP BY are a problem), you want to avoid that. This is a place where a hint might work well.

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I was going to suggest the NOEXPAND hint! I couldn't see anywhere in the thread to see what edition of SQL Server the OP is using. Unless it's enterprise edition the optimiser won't consider the index on the view when it's costing the query. Unless i've misunderstood the way the optimiser works with indexed views.

Thanks,


Simon



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ScottPletcher
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First, I assume you've all met all the oodles of restrictions for an indexed view; you might want to verify that using Books Online "CREATE INDEX", "Remarks", "Indexed Views" as a guied.

Also, GROUP BY in the base query in exactly the same order as the clus index will be:


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 ...



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Gazareth (1/23/2013)

If you change your indexed view definition to:

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

) go

I think you'll see this view being used in place of the table.

Cheers


You should take this advice.

Or, better, merge YEAR and MONTH columns together:

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



And make this column the first one in the clustered index.
Then you may just select
WHERE MonthOfYear between @StartOfThePeriod AND @EndOfThePeriod

Than you may just use
Go


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