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Jeff Moden
Jeff Moden
Posted Saturday, October 11, 2008 11:33 AM
SSC-Dedicated
Group: General Forum Members
Last Login: Yesterday @ 9:57 PM
Points: 32,893,
Visits: 26,771
Outstanding explanation, Kenney.
On the recursive thing... do keep in mind that recurssion is nothing more than a loop and has the same performance impedements as a loop. In other words, it IS a form of RBAR. There are many ways to avoid the use of any type of RBAR on many things. Even when it comes to Hierarchies, there are some really good ways to precalculate the hierarchy (nested sets) and then do the lookups using set based technologies instead of RBAR.
--Jeff Moden
"
RBAR
is pronounced "ree-bar" and is a "Modenism" for "
R
ow-
B
y-
A
gonizing-
R
ow".
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."
For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
Post #584410
Kenney Hill
Kenney Hill
Posted Saturday, October 11, 2008 10:59 PM
SSC Veteran
Group: General Forum Members
Last Login: Friday, May 17, 2013 4:18 PM
Points: 299,
Visits: 110
Thank you Jeff.
And thanks for pointing out the RBAR aspect of recursive queries. I'm still not very good at spotting hidden RBAR, and you are the master of that subject. :) I remember reading an article by you about triangular joins being RBAR, it was very enlightening.
Do you happen to have a posted example of a non-RBAR hierarchal query? I'd really like to see how that is done. I've been very impressed by your postings that I have read.
Thanks again,
Kenney
Post #584499
Carla Wilson-484785
Carla Wilson-484785
Posted Monday, October 13, 2008 8:00 AM
Ten Centuries
Group: General Forum Members
Last Login: Wednesday, May 15, 2013 1:00 PM
Points: 1,349,
Visits: 1,737
Kenny,
Thanks for pointing out the performance implications of using a CTE versus a temp table multiple times in a query.
Post #584876
Jeff Moden
Jeff Moden
Posted Monday, October 13, 2008 8:34 AM
SSC-Dedicated
Group: General Forum Members
Last Login: Yesterday @ 9:57 PM
Points: 32,893,
Visits: 26,771
Kenney Hill (10/11/2008)
Thank you Jeff.
And thanks for pointing out the RBAR aspect of recursive queries. I'm still not very good at spotting hidden RBAR, and you are the master of that subject. :) I remember reading an article by you about triangular joins being RBAR, it was very enlightening.
Do you happen to have a posted example of a non-RBAR hierarchal query? I'd really like to see how that is done. I've been very impressed by your postings that I have read.
Thanks again,
Kenney
You bet...
http://www.ibase.ru/devinfo/DBMSTrees/sqltrees.html
http://www.codeproject.com/KB/database/nestedsets.aspx
What I end up doing is preserving both models on hierarchies that don't change much (most don't). People have an easier time maintaining and thinking about the adjacency model and the code runs better on the nested set model.
--Jeff Moden
"
RBAR
is pronounced "ree-bar" and is a "Modenism" for "
R
ow-
B
y-
A
gonizing-
R
ow".
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."
For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
Post #584916
mohd.nizamuddin
mohd.nizamuddin
Posted Friday, September 11, 2009 3:27 AM
Old Hand
Group: General Forum Members
Last Login: Friday, July 29, 2011 4:14 AM
Points: 318,
Visits: 198
Abhijit,
Great Article.
Moreover, nicely explained and modified by Jeff.
Really appriciate.
Post #786219
Jeff Moden
Jeff Moden
Posted Friday, September 11, 2009 4:07 PM
SSC-Dedicated
Group: General Forum Members
Last Login: Yesterday @ 9:57 PM
Points: 32,893,
Visits: 26,771
Thank you for the feedback... Kenny actually did all the heavy lifting, though.
Thanks, Ken.
--Jeff Moden
"
RBAR
is pronounced "ree-bar" and is a "Modenism" for "
R
ow-
B
y-
A
gonizing-
R
ow".
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."
For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
Post #786755
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