How to optimize case statement

Question

How to optimize case statement

thbaig

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Points: 3003
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January 17, 2014 at 8:06 am

#151312

Hi,
I have several rule on my item name to compute its gender. I know this structure might need to tune , but currently can't change:(
I wrote sql and its working perfect. But as it has many cases and left and right functions,there are more conditions but I am posting just basic one. I would love to optimize my code.
Do you have any suggestion to modify my TSQL ?
Table tblBrand
BrandId int identity,
BrandName varchar(3)
Sample Data
BrandId BrandName
1 brand1
2 brand2
3 brand3
4 brand4
5 brand5
6 brand5
table tblItem
ItemId int identity,
ItemName varchar(10),
BrandId int (FK->tblBrand.BrandId)
ItemId ItemName BrandId
1YItem 1
2LItem 1
3abc 1
4 ItemB 6
.........
.........
SELECT
IT.ItemName,
-- Case for Gender
CASE WHEN br.BrandName IN ( 'brand1', 'brand2', 'brand3' )
AND LEFT(it.ItemName, 1) = 'L' THEN 'Ladies'
WHEN br.BrandName IN ( 'brand1', 'brand2', 'brand3' )
AND LEFT(it.ItemName, 1) = 'Y' THEN 'Youth'
WHEN br.BrandName IN ( 'brand1', 'brand2', 'brand3' )
AND (LEFT(it.ItemName, 1) <> 'Y'
OR LEFT(it.ItemName, 1) <> 'L'
) THEN 'Adult'
WHEN br.BrandName = 'brand4' THEN 'Adult'
WHEN br.BrandName = 'brand5'
AND RIGHT(it.ItemName,1) IN ( 'B', 'Y' )
THEN 'Youth'
WHEN br.BrandName = 'brand6'
AND RIGHT(it.ItemName,1) = 'B' THEN 'Youth'
WHEN br.BrandName = 'brand6'
AND RIGHT(it.ItemName,1) = 'L' THEN 'Ladies'
ELSE ''
END AS Gender, -- Case for Gender end
FROM tblBrand br
INNER JOIN tblItem it ON it.BrandId = br.BrandId

Viewing 5 posts - 1 through 4 (of 4 total)

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Luis Cazares SSC Guru Points: 183706 More actions · Answer 1

I'm not sure if it will help performance wise, but it might improve readability if you include your cases in a lookup table (or cte).

Luis C.
General Disclaimer:
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Dwain Camps SSC Guru Points: 86948 More actions · Answer 2

Or you could put this convoluted Gender computation into a computed column.

My mantra: No loops! No CURSORs! No RBAR! Hoo-uh![/I]
My thought question: Have you ever been told that your query runs too fast?

My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.

Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

thbaig1 (1/17/2014)
Hi,
I have several rule on my item name to compute its gender. I know this structure might need to tune , but currently can't change:(
I wrote sql and its working perfect. But as it has many cases and left and right functions,there are more conditions but I am posting just basic one. I would love to optimize my code.

Why do you think it needs tuning? Have you run the query with and without the case and seen what the time difference is? If it enough of a time difference and is the overall query enough of a performance problem to warrant looking at?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 4

Like Gail, I don't think this expression is going to have much impact on performance. Maintainability is another story - updating n queries to account for product changes leaves you wide open to errors. Put the code into an iTVF so you have a common code block for all of the queries which return 'gender' (I'd call it 'fitting' personally because 'youth' isn't a gender). Something like this:

CREATE FUNCTION IF_BrandItemFitting

(

@BrandName VARCHAR(20),

@ItemName VARCHAR(20)

)

RETURNS TABLE

AS

RETURN

(

SELECT [Fitting] = CASE

WHEN @BrandName IN ( 'brand1', 'brand2', 'brand3' )

AND LEFT(@ItemName, 1) = 'L'

THEN 'Ladies'

WHEN @BrandName IN ( 'brand1', 'brand2', 'brand3' )

AND LEFT(@ItemName, 1) = 'Y'

THEN 'Youth'

WHEN @BrandName IN ( 'brand1', 'brand2', 'brand3' )

--AND (LEFT(@ItemName, 1) <> 'Y' -- not strictly needed - see first 2 cases

--OR LEFT(@ItemName, 1) <> 'L')

THEN 'Adult'

WHEN @BrandName = 'brand4'

THEN 'Adult'

WHEN @BrandName = 'brand5'

AND RIGHT(@ItemName,1) IN ( 'B', 'Y' )

THEN 'Youth'

WHEN @BrandName = 'brand6'

AND RIGHT(@ItemName,1) = 'B'

THEN 'Youth'

WHEN @BrandName = 'brand6'

AND RIGHT(@ItemName,1) = 'L'

THEN 'Ladies'

ELSE NULL -- NULL, not ''

END

)

GO

Use it like this:

SELECT

IT.ItemName,

bf.fitting

FROM tblBrand br

INNER JOIN tblItem it

ON it.BrandId = br.BrandId

CROSS APPLY dbo.IF_BrandItemFitting (br.BrandName, it.ItemName) bf

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
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