SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


Delete Duplicate values


Delete Duplicate values

Author
Message
Jeff Moden
Jeff Moden
SSC Guru
SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)

Group: General Forum Members
Points: 206534 Visits: 41959
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 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.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
Kenney Hill
Kenney Hill
Mr or Mrs. 500
Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)Mr or Mrs. 500 (594 reputation)

Group: General Forum Members
Points: 594 Visits: 250
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. Smile 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
Carla Wilson-484785
Carla Wilson-484785
SSCrazy
SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)SSCrazy (2.3K reputation)

Group: General Forum Members
Points: 2272 Visits: 1951
Kenny,
Thanks for pointing out the performance implications of using a CTE versus a temp table multiple times in a query.
Jeff Moden
Jeff Moden
SSC Guru
SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)

Group: General Forum Members
Points: 206534 Visits: 41959
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. Smile 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 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.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
mohd.nizamuddin
mohd.nizamuddin
Mr or Mrs. 500
Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)Mr or Mrs. 500 (552 reputation)

Group: General Forum Members
Points: 552 Visits: 198
Abhijit,
Great Article.

Moreover, nicely explained and modified by Jeff.
Really appriciate.
:-)
Jeff Moden
Jeff Moden
SSC Guru
SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)SSC Guru (206K reputation)

Group: General Forum Members
Points: 206534 Visits: 41959
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 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.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search