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NULL Values and Joins


NULL Values and Joins

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philip.cullingworth
philip.cullingworth
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Carlo Romagnano (12/20/2010)

Please, read carefully the question: it asks how many rows are in the results and what is the value of column "d" on the last row.


Blush That will teach me. I read the code and assumed what the actual question would be. Can I blame being up in the middle of the night defrosting water pipes?
vk-kirov
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philip.cullingworth (12/20/2010)
But Answer D is
7 rows where column d = three

I only have 1 row where column d = three Ermm

I had read the answers several times before I realized there were some skipped words: "7 rows where [the value of] column d [in the last row] = three" Hehe
ian.grace
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I don't understand how the first transaction could succeed given the attempt to insert the null value into the not-null field "a". Also, why is the last insert of the second transaction, VALUES(2 ,'one'), invalid? Help, I'm confused.
Carlo Romagnano
Carlo Romagnano
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ian.grace (12/20/2010)
I don't understand how the first transaction could succeed given the attempt to insert the null value into the not-null field "a". Also, why is the last insert of the second transaction, VALUES(2 ,'one'), invalid? Help, I'm confused.

As posted above by vk-kirov and others, the explanation is terrible with a lot of mistakes.

I run on tuttopodismo
Koen Verbeeck
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ian.grace (12/20/2010)
I don't understand how the first transaction could succeed given the attempt to insert the null value into the not-null field "a". Also, why is the last insert of the second transaction, VALUES(2 ,'one'), invalid? Help, I'm confused.


The first transaction succeeds because it is an explicit transaction. Those will only fail if you explicitly issue a ROLLBACK statement, which isn't the case. Since a COMMIT was issued, the 2 other INSERTS in the transaction are committed to the database.


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ian.grace
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Thanks for that
Marek Grzymala
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so the correct answer should be: "7 rows where the last row's column d = three", not: "7 rows where column d = three", going by the way the question is phrased none of the answers are correct.
sjimmo
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Good Monday morning question - math test and logic while clearing the cobwebs and trying to get my first cup of coffee;-)

Made me think, question and reread.

Steve Jimmo
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ronmoses
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I'm completely confused by this explanation. Especially this part:

However, since the last insert in the second Transaction was invalid, no rows were inserted into table2. So B not C is the correct answer.

But D is given as the correct answer, and as far as I can tell, rows are inserted into table2. What am I missing?

Ron

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SanDroid
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I agree that if you read the question the answer is obvious.

However there is a HUGE typo in the explination...
B not C is the Answer?

Disapointing.
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