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Caution with EXCEPT


Caution with EXCEPT

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jdurandt
jdurandt
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That's interesting

I benchmarked EXCEPT vs WHERE NOT IN (SELECT .....), and for my dataset, server, DB version etc. the performance results were equivalent, or biased towards EXCEPT.

Can you give more details about your scenario?
jdurandt
jdurandt
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I find that an easier way to get the list of columns is to drag them from the object explorer in SSMS. If you expand the table object's columns list, you can then drag the "Columns" parent entry into a query window, to get the comma seperated list of columns.

This works for some other items too.
Mike DiRenzo
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Bravo! What a great catch. You have my 5 star vote.

-Mike
Jeff Moden
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jdurandt (1/18/2010)
That's interesting

I benchmarked EXCEPT vs WHERE NOT IN (SELECT .....), and for my dataset, server, DB version etc. the performance results were equivalent, or biased towards EXCEPT.

Can you give more details about your scenario?


Can you post your benchmark code, please?

--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.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is usually not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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Jeff Moden
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Nicely done, Stephen. Well written and straight to the point.

--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.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is usually not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
ChrisM@Work
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Some articles are well worth reading twice.
I've spent all afternoon working for the first time with EXCEPT instead of the usual LEFT JOIN and checking for NULL, and it's taken half the keystrokes with no noticeable performance cost. Thanks!

“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps
Joseph M. Steinbrunner
Joseph M. Steinbrunner
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Good explanation. I saw what was coming on your first SQL example right away (as some others did) when the use of "SELECT *" was there.
shannonjk
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Good article Stephen I am going to write the points down of this article in some notes I am gathering.

I wish that they would design the inverse of the INTERSECT operator. As it will show you all the rows matching from both sides of the statement. If they had a NOT INTERSECT it seems like it would return the results of all the aforementioned UNION queries.

Link to my blog http://notyelf.com/
gchornenkyy
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For bugmenot-573553:
Try do develop correct indexes - it may help
shannonjk
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Stephen,

Again a great article, but if I could throw in one little tiny technicality to this I would feel much better :-D

While I realize the emphasis of your article was against 2 tables, and therefore you wrote it as such, I would like to point out that the left and right side of EXCEPT, INTERSECT, and UNION Operators is the comparison of 'query results' and not 'tables'. Though a seemingly minor point, I felt necessary to point it out :-D

Link to my blog http://notyelf.com/
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