Order of GROUP BY - does it matter?

[rcamarda]

Does the order of columns make a difference in the GROUP BY?
Woulde GROUP BY A, B, C
return different results than
GROUP BY C,A,B ?

[Dan Guzman]

No.

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Hope this helps.

Dan Guzman
SQL Server MVP

"rcamarda" <ro*****@hotmail.comwrote in message
news:11**********************@f16g2000cwb.googlegr oups.com...

Does the order of columns make a difference in the GROUP BY?
Woulde GROUP BY A, B, C
return different results than
GROUP BY C,A,B ?

[Roy Harvey]

On 23 Oct 2006 05:23:26 -0700, "rcamarda" <ro*****@hotmail.comwrote:

>Does the order of columns make a difference in the GROUP BY?
Woulde GROUP BY A, B, C
return different results than
GROUP BY C,A,B ?

There is no difference. The set of rows returned is identical.

For an exception of sorts you have to go back to release 6.5 and
earlier. With those releases, if an ORDER BY was not provided, the
result set always ended up sorted on the GROUP BY; in that case the
same rows would be returned but the sequence would have changed
depending on the arrangement of the items in the GROUP BY clause. Many
people came to depend on that undocumented behavior and found there
were problems when they upgraded.

Roy Harvey
Beacon Falls, CT

[David Portas]

rcamarda wrote:

Does the order of columns make a difference in the GROUP BY?
Woulde GROUP BY A, B, C
return different results than
GROUP BY C,A,B ?

In SQL Server 200x I can only think of one instance where it does make
a difference. If you use the ROLLUP clause then the values will get
summarized based on the order specified in the GROUP BY. This means
you'll see an entirely different set of totals depending on the GROUP
BY order.

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David Portas, SQL Server MVP

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Including CREATE TABLE and INSERT statements usually helps.
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http://msdn2.microsoft.com/library/m...S,SQL.90).aspx
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