Caution with EXCEPT

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Caution with EXCEPT

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jdurandt

Posted Monday, January 18, 2010 8:20 AM

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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?

Post #849195

jdurandt

Posted Monday, January 18, 2010 8:22 AM

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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.

Post #849196

Mike DiRenzo

Posted Monday, January 18, 2010 8:34 AM

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Bravo! What a great catch. You have my 5 star vote.

-Mike

Post #849209

Jeff Moden

Posted Monday, January 18, 2010 9:53 AM

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jdurandt (1/18/2010)

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."

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 #849264

Jeff Moden

Posted Monday, January 18, 2010 9:56 AM

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

--Jeff Moden

Post #849268

ChrisM@Work

Posted Monday, January 18, 2010 10:17 AM

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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

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Joseph M. Steinbrunner

Posted Monday, January 18, 2010 12:25 PM

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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.

Post #849326

shannonjk

Posted Monday, January 18, 2010 12:48 PM

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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/

Post #849343

gchornenkyy

Posted Monday, January 18, 2010 12:56 PM

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For bugmenot-573553:
Try do develop correct indexes - it may help

Post #849346

shannonjk

Posted Monday, January 18, 2010 2:20 PM

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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 BigGrin

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 BigGrin

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

Post #849401

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