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Fun with IDENTITY - Part I


Fun with IDENTITY - Part I

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SQLRNNR
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Thanks for the question.



Jason AKA CirqueDeSQLeil
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Mike Is Here
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UMG Developer (9/28/2010)
I agree, nice question, but it would have been even better with a fourth option: 1-Boston;2-New Delhi

Without that option it was really a test of transactions, not of IDENTITY. (Maybe that was the point to through people off the scent?) ;-)


Agreed, reading the question I was thinking would New Delhi be 2 or 3. When 2 was not an option that answer was clear.
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Good question - after the fun with transactions, nobody should have gotten this one wrong:-P

Steve Jimmo
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Easy one. With Begin and Rollback Transaction included in question it's easy to select correct answer.

SQL DBA.
Daniel Bowlin
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It's nice to get a QoTD once in a while without a trick. Nice question.
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I agree, a forth option of 1-Boston;2-New Delhi would have made the question better. With a forth option, I would have had to think more about the impact of a rolled back transaction has on the Identity values to get the correct answer.

Good question though.



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edit - replied to the wrong topic!
Amy.G
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Why would you ever use "rollback transaction" unless with an "if @@error" statement?
TomThomson
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The correct answer "It depends" isn't available as an option.

How many rows are produced depends on the IMPLICIT_TRANSACTIONS setting.

If ANSI_DEFAULTS or IMPLICIT_TRANSACTIONS have been set on, this code will produce no rows (just an error message for the third insert, which is an attempt to insert into a nonexistent table). The BEGIN TRAN statement won't open a transaction because there is already an active transaction.

But most connections default to autocommit mode ( so IMPLICIT_TRANSACTIONS is off) so the code will produce 2 rows, as in the supposedly correct answer.

As no rows wasn't an option, it was possible to deduce that IMPLICIT_TRANSACTIONS had to be OFF so that the 2-row answer was the one expected by the person who set the question.

Tom

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