RE: DML on dual?

John,  

Since I didn't have Tom's book with me, I decided to check his website. Probably had my facts confused. Right author, wrong example? Anyway, it appears that SQL*Plus connections generate this same statement.  

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:15628139 56388
<http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1562813 956388>
SELECT NULL FROM DUAL FOR UPDATE NOWAIT; December 27, 2005  

David

-----Original Message-----
From: Taft, David
Sent: Thursday, April 12, 2007 3:30 PM
To: 'darrah.john_at_gmail.com'; Dave.Herring_at_acxiom.com Cc: oracle-l_at_freelists.org
Subject: RE: DML on dual?

John,  

Hmmm, my memory may not be serving me too well here, but this reminds me of something I read in Tom Kyte's newest book. I don't have the book with me, so I can't look it up, but I think he had an example of some sort of home-grown concurrency control mechanism. Probably an example of how not to code. Anyway, I believe the example was such that a session had to hold this lock for the code to proceed. Darn, the one day I don't have that book on hand.  

Cheers,  

David Taft

From: John Darrah [mailto:darrah.john_at_gmail.com]

I've seen several oracle trace files that have the statement "SELECT 1 FROM DUAL FOR UPDATE NOWAIT" I have no idea what the purpose of that statement is but it probably explains what you are seeing.

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