Does the physical position of FK columns matter?

Question

Does the physical position of FK columns matter?

Jeremiah Peschka

SSChasing Mays

Points: 640
More actions
October 3, 2008 at 12:48 pm

#193958

Essentially, I'm curious if the position of an FK column matters for performance.
That is, is:
CREATE TABLE User (
UserId INT IDENTITY(1,1) PRIMARY KEY,
UserTypeId INT REFERENCES UserType(UserTypeId),
-- 50 columns
);
any faster to select the UserTypes from than
CREATE TABLE User (
UserId INT IDENTITY(1,1) PRIMARY KEY,
-- 50 columns
UserTypeId INT REFERENCES UserType(UserTypeId)
);
Jeremiah Peschka
Microsoft SQL Server MVP
Managing Director - Brent Ozar PLF, LLC

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Adi Cohn-120898 SSC-Dedicated Points: 33944 More actions · Answer 1

jeremiah.peschka (10/3/2008)
Essentially, I'm curious if the position of an FK column matters for performance.
That is, is:
CREATE TABLE User (
UserId INT IDENTITY(1,1) PRIMARY KEY,
UserTypeId INT REFERENCES UserType(UserTypeId),
-- 50 columns
);
any faster to select the UserTypes from than
CREATE TABLE User (
UserId INT IDENTITY(1,1) PRIMARY KEY,
-- 50 columns
UserTypeId INT REFERENCES UserType(UserTypeId)
);

The location of the foreign key column in the create table statement has nothing to do with performance. By the way, the physical order of the columns on the disk is not necessarily the same as the logical order of the columns.

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Gail Shaw SSC Guru Points: 1004514 More actions · Answer 2

No. The declared order of columns has no effect on anything other than the order they're returned in a select * query. The order defined doesn't even define the physical storage order.

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

Jeremiah Peschka SSChasing Mays Points: 640 More actions · Answer 3

Thanks for clarifying that for me.

Jeremiah Peschka
Microsoft SQL Server MVP
Managing Director - Brent Ozar PLF, LLC

Jeff Moden SSC Guru Points: 1004635 More actions · Answer 4

And, yet, we so no testing nor references to Microsoft articles on the subject... does anyone have proof one way or the other? 😉

--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.

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