SQL SubQuery Slow

I have a transactional database table.  I would like to retrieve data for current years and then previous years.  The query itself takes 2 seconds to run returning about 25,000 rows.  Issue is that when I created a subquery from same table for previous year and so on, it gets really slow.  My 2 seconds turn into a minute, and then 5 minutes, and then so on and so on.

Is there a better way to make it faster?

Here's what my sql query code looks like.
SELECT	DISTINCT IT.ITEM_ID, A.AVG_COST_1, B.AVG_COST_2, C.AVG_COST_3
FROM	INVENTORY_TRANSACTION IT

		LEFT OUTER JOIN
		(
		SELECT	IT.ITEM_ID, AVG(IT.COST) AVG_COST_1
		FROM	INVENTORY_TRANSACTION IT
		WHERE	DATEPART(YEAR, CREATE_DATE) = DATEPART(YEAR, GETDATE())
		GROUP BY IT.ITEM_ID
		) A ON A.ITEM_ID = IT.ITEM_ID
		
		LEFT OUTER JOIN
		(
		SELECT	IT.ITEM_ID, AVG(IT.COST) AVG_COST_2
		FROM	INVENTORY_TRANSACTION IT
		WHERE	DATEPART(YEAR, CREATE_DATE) = DATEPART(YEAR, GETDATE()) -1
		GROUP BY IT.ITEM_ID
		) B ON B.ITEM_ID = IT.ITEM_ID
		
		LEFT OUTER JOIN
		(
		SELECT	IT.ITEM_ID, AVG(IT.COST) AVG_COST_3
		FROM	INVENTORY_TRANSACTION IT
		WHERE	DATEPART(YEAR, CREATE_DATE) = DATEPART(YEAR, GETDATE()) -2
		GROUP BY IT.ITEM_ID
		) C ON C.ITEM_ID = IT.ITEM_ID

WHERE	DATEPART(YEAR, CREATE_DATE) = DATEPART(YEAR, GETDATE())
ORDER BY IT.ITEM_ID

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Here's my expected result:
example
holemaniaAsked:
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Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
Can you confirm which version of SQL Server you are on please.
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Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
How about this:

With MyTable as
(select Item_ID, DATEPART(YEAR, GETDATE()) - DATEPART(YEAR, CREATE_DATE) as myYearDiff, Avg(Cost) as AvgCost
from Inventory_Transaction
group by Item_ID, DATEPART(YEAR, CREATE_DATE)),
myPvt as
(Select *
from MyTable
pivot (sum(AvgCost) for myYearDiff in ([0], [1], [2])) as MyP)
select Item_ID, [0] as ThisYear, [1] as LastYear, [2] as YearBeforeLast
from myPvt

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0
Vitor MontalvãoMSSQL Senior EngineerCommented:
You can create a View and use the View in the SELECT.
CREATE VIEW AverageCost AS 
		SELECT	ITEM_ID, DATEPART(YEAR, CREATE_DATE) ITEM_YEAR, AVG(COST) AVG_COST
		FROM	INVENTORY_TRANSACTION
		GROUP BY ITEM_ID, DATEPART(YEAR, CREATE_DATE)

SELECT	IT.ITEM_ID, A.AVG_COST_1, B.AVG_COST_2, C.AVG_COST_3
FROM	INVENTORY_TRANSACTION IT
		LEFT OUTER JOIN
		(
		SELECT	ITEM_ID, AVG_COST AVG_COST_1
		FROM	AverageCost
		WHERE	ITEM_YEAR = DATEPART(YEAR, GETDATE())
		) A ON A.ITEM_ID = IT.ITEM_ID
		
		LEFT OUTER JOIN
		(
		SELECT	ITEM_ID, AVG_COST AVG_COST_2
		FROM	AverageCost
		WHERE	ITEM_YEAR = DATEPART(YEAR, GETDATE())-1
		) B ON B.ITEM_ID = IT.ITEM_ID
		
		LEFT OUTER JOIN
		(
		SELECT	ITEM_ID, AVG_COST AVG_COST_2
		FROM	AverageCost
		WHERE	ITEM_YEAR = DATEPART(YEAR, GETDATE())-2
		) C ON C.ITEM_ID = IT.ITEM_ID

WHERE	DATEPART(YEAR, CREATE_DATE) = DATEPART(YEAR, GETDATE())
ORDER BY IT.ITEM_ID

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0
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Scott PletcherSenior DBACommented:
To gain efficiency:
1) don't use a function on the table column
2) get all years at once, rather than using a separate query for each year
SELECT  ITEM_ID,
            MAX(CASE WHEN ITEM_YEAR = DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()), 0) THEN AVG_COST END) AS AVG_COST_1,
            MAX(CASE WHEN ITEM_YEAR = DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()) - 1, 0) THEN AVG_COST END) AS AVG_COST_2,
            MAX(CASE WHEN ITEM_YEAR = DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()) - 2, 0) THEN AVG_COST END) AS AVG_COST_3            
FROM (
		SELECT	IT.ITEM_ID, DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()), 0) AS ITEM_YEAR, AVG(IT.COST) AVG_COST
		FROM	INVENTORY_TRANSACTION IT
		WHERE	IT.CREATE_DATE >= DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()) - 2, 0) AND
		        IT.CREATE_DATE < DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()) + 1, 0)
		GROUP BY IT.ITEM_ID, DATEADD(YEAR, DATEDIFF(YEAR, 0, GETDATE()), 0)
) AS subquery1
GROUP BY ITEM_ID

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0

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PortletPaulfreelancerCommented:
and
3) ensure that INVENTORY_TRANSACTION.CREATE_DATE is indexed

If you adopt Scott Pletcher's suggested query, and then still have performance issues, please
a. identify what indexes do exist on the table
b. prepare an execution plan and attach the .sqlplan file here
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holemaniaAuthor Commented:
Thank you.  That worked very well and took only seconds to run.
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