Where exists vs Where in

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Where exists vs Where in

Mark Eckeard

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July 1, 2012 at 6:56 pm

#258734

If I understand it correctly, "exists" stops evaluating once it hits the first true whereas "in" keeps going. To me, this makes "exists" the obvious choice between the 2 but I still see queries using both and I'm not sure why.
Should there be a fast and simple rule for using one over the other or does it depend on the data in the table or the query being run?
Thanks,
Mark

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Rick Krueger SSC Eights! Points: 856 More actions · Answer 1

This blog post illustrates one big difference: SQL Server: JOIN vs IN vs EXISTS - the logical difference

Rick Krueger

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rhythmk SSCertifiable Points: 7271 More actions · Answer 2

Mark Eckeard (7/1/2012)

If I understand it correctly, "exists" stops evaluating once it hits the first true whereas "in" keeps going. To me, this makes "exists" the obvious choice between the 2 but I still see queries using both and I'm not sure why.

No this is not always true for every case.

Please have a look on below article by Gilla Monster.

http://sqlinthewild.co.za/index.php/2010/04/27/in-exists-and-join-a-roundup/">

http://sqlinthewild.co.za/index.php/2010/04/27/in-exists-and-join-a-roundup/

--rhythmk
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To post your question use below link

https://www.sqlservercentral.com/articles/forum-etiquette-how-to-post-datacode-on-a-forum-to-get-the-best-help
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rhythmk SSCertifiable Points: 7271 More actions · Answer 3

Also have a look on below article.

http://sqlinthewild.co.za/index.php/2009/08/17/exists-vs-in/">

http://sqlinthewild.co.za/index.php/2009/08/17/exists-vs-in/

--rhythmk
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To post your question use below link

https://www.sqlservercentral.com/articles/forum-etiquette-how-to-post-datacode-on-a-forum-to-get-the-best-help
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Jeff Moden SSC Guru Points: 1004292 More actions · Answer 4

rhythmk (7/3/2012)
Also have a look on below article.
http://sqlinthewild.co.za/index.php/2009/08/17/exists-vs-in/">
http://sqlinthewild.co.za/index.php/2009/08/17/exists-vs-in/

That link appears to be broken or incomplete.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 5

http://sqlinthewild.co.za/index.php/2009/08/17/exists-vs-in/

http://sqlinthewild.co.za/index.php/2010/04/27/in-exists-and-join-a-roundup/

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

Jeff Moden SSC Guru Points: 1004292 More actions · Answer 6

Mark Eckeard (7/1/2012)
If I understand it correctly, "exists" stops evaluating once it hits the first true whereas "in" keeps going. To me, this makes "exists" the obvious choice between the 2 but I still see queries using both and I'm not sure why.
Should there be a fast and simple rule for using one over the other or does it depend on the data in the table or the query being run?
Thanks,
Mark

Keeping in mind that INNER JOIN will allow dupes to occur and the other two will not (and a couple of other differences highlighted in Gail's article), if you're looking for a speed advantage of WHERE EXISTS compared to WHERE IN, there really isn't one. Here's a test...

-----------------------------------------------------------------------------------------------------------------------

IF OBJECT_ID('tempdb.dbo.JBMTest','U') IS NOT NULL DROP TABLE dbo.JBMTest;

IF OBJECT_ID('tempdb..#MyInTable','U') IS NOT NULL DROP TABLE #MyInTable;

GO

RAISERROR('Creating and populating the test table...',0,1) WITH NOWAIT;

--===== Create and populate a 1,000,000 row test table.

-- Column "RowNum" has a range of 1 to 1,000,000 unique numbers

-- Column "SomeInt" has a range of 1 to 50,000 non-unique numbers

-- Column "SomeLetters2" has a range of "AA" to "ZZ" non-unique 2 character strings

-- Column "SomeMoney has a range of 0.0000 to 99.9999 non-unique numbers

-- Column "SomeDate" has a range of >=01/01/2000 and <01/01/2010 non-unique date/times

-- Column "SomeCSV" contains 'Part01,Part02,Part03,Part04,Part05,Part06,Part07,Part08,Part09,Part10'

-- for all rows.

-- Column "SomeHex12" contains 12 random hex characters (ie, 0-9,A-F)

-- Jeff Moden

SELECT TOP 1000000

RowNum = IDENTITY(INT,1,1),

SomeInt = ABS(CHECKSUM(NEWID()))%50000+1,

SomeLetters2 = CHAR(ABS(CHECKSUM(NEWID()))%26+65)

+ CHAR(ABS(CHECKSUM(NEWID()))%26+65),

SomeCSV = CAST('Part01,Part02,Part03,Part04,Part05,Part06,Part07,Part08,Part09,Part10' AS VARCHAR(80)),

SomeMoney = CAST(ABS(CHECKSUM(NEWID()))%10000 /100.0 AS MONEY),

SomeDate = CAST(RAND(CHECKSUM(NEWID()))*3653.0+36524.0 AS DATETIME),

SomeHex12 = RIGHT(NEWID(),12)

INTO dbo.JBMTest

FROM sys.all_columns t1

CROSS JOIN sys.all_columns t2

RAISERROR('Adding the PK...',0,1) WITH NOWAIT;

--===== A table is not properly formed unless a unique clustered index has been assigned

ALTER TABLE dbo.JBMTest

ADD PRIMARY KEY CLUSTERED (RowNum)

RAISERROR('Creating the WHERE IN table...',0,1) WITH NOWAIT;

--===== Create a table with some "WHERE IN" values

SELECT TOP 1000

IDENTITY(INT,1,1) AS RowNum,

ABS(CHECKSUM(NEWID()))%50000+1 AS SomeInt

INTO #MyInTable

FROM sys.all_columns t1

RAISERROR('Adding another index to the test table...',0,1) WITH NOWAIT;

----===== Add an index to the larger table

CREATE INDEX IX_JBMTest_SomeInt

ON dbo.JBMTest (SomeInt)

----===== A table is not properly formed unless a Primary Key has been assigned

-- ALTER TABLE #MyInTable

-- ADD PRIMARY KEY CLUSTERED (RowNum)

----===== Add an index to it

-- CREATE INDEX IX_MyInTable_SomeInt

-- ON #MyInTable (SomeInt)

-----------------------------------------------------------------------------------------------------------------------

IF OBJECT_ID('tempdb..#MyHead1','U') IS NOT NULL DROP TABLE #MyHead1;

IF OBJECT_ID('tempdb..#MyHead2','U') IS NOT NULL DROP TABLE #MyHead2;

IF OBJECT_ID('tempdb..#MyHead3','U') IS NOT NULL DROP TABLE #MyHead3;

--===== THE TEST CODE

RAISERROR('========== INNER JOIN ==================================================',0,1) WITH NOWAIT;

SET STATISTICS TIME ON

SELECT DISTINCT t.*

INTO #MyHead1

FROM dbo.JBMTest t

INNER JOIN #MyInTable i

ON t.SomeInt = i.SomeInt

SET STATISTICS TIME OFF

GO

RAISERROR('========== WHERE IN ==================================================',0,1) WITH NOWAIT;

SET STATISTICS TIME ON

SELECT t.*

INTO #MyHead2

FROM dbo.JBMTest t

WHERE t.SomeInt IN (SELECT SomeInt FROM #MyInTable)

SET STATISTICS TIME OFF

GO

RAISERROR('========== WHERE EXISTS ==================================================',0,1) WITH NOWAIT;

SET STATISTICS TIME ON

SELECT t.*

INTO #MyHead3

FROM dbo.JBMTest t

WHERE EXISTS (SELECT 1 FROM #MyInTable i WHERE t.SomeInt = i.SomeInt)

SET STATISTICS TIME OFF

GO

-----------------------------------------------------------------------------------------------------------------------

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Mark Eckeard Hall of Fame Points: 3462 More actions · Answer 7

Thanks for all the links. I'll read them later this evening when I get home.

Thanks,

Mark