exceptional logic

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exceptional logic

BenWard

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October 10, 2011 at 8:11 pm

#244352

Comments posted to this topic are about the item exceptional logic
Ben
^ Thats me!
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01010111011010000110000101110100 01100001 0110001101101111011011010111000001101100011001010111010001100101 01110100011010010110110101100101 011101110110000101110011011101000110010101110010
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October 11, 2011 at 1:26 am

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Ron McCullough SSC Guru Points: 63877 More actions · Answer 1

Nice question

If everything seems to be going well, you have obviously overlooked something.

Ron

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Andre Guerreiro SSCertifiable Points: 7319 More actions · Answer 2

That looks and executes right... but I can't understand why the result is not only the number 4.

After the EXCEPT, only the number 4 remains. So where does that 5 come from in the INTERSECT part?

I'm testing it in SSMS but I don't get it. :unsure:

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Andre Guerreiro Neto

Database Analyst
http://www.softplan.com.br
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SQLRNNR SSC Guru Points: 281334 More actions · Answer 3

Thanks

Jason...AKA CirqueDeSQLeil
_______________________________________________
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SQL RNNR
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vk-kirov SSCertifiable Points: 7686 More actions · Answer 4

Nice question

codebyo (10/10/2011)
That looks and executes right... but I can't understand why the result is not only the number 4.
After the EXCEPT, only the number 4 remains. So where does that 5 come from in the INTERSECT part?

Please be aware that the INTERSECT operand has higher precedence than the EXCEPT and UNION operands (http://msdn.microsoft.com/en-us/library/ms188055.aspx):

EXCEPT and INTERSECT (Transact-SQL)
Remarks
If EXCEPT or INTERSECT is used together with other operators in an expression, it is evaluated in the context of the following precedence:
1. Expressions in parentheses
2. The INTERSECT operand
3. EXCEPT and UNION evaluated from left to right based on their position in the expression

So, the code given in the QOTD is equal to the following pseudocode:

( (1, 2, 5)

union

(1, 2, 4) )

except

( (1, 2, 5)

intersect

(1, 2, 4) )

Which is equal to the following pseudocode:

(1, 2, 4, 5)

except

(1, 2)

Which gives us "4, 5" as a result.

Nakul Vachhrajani SSChampion Points: 10283 More actions · Answer 5

This is a good, useful QotD. Thank-you!

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Nakul Vachhrajani.
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palotaiarpad SSCertifiable Points: 5617 More actions · Answer 6

That was a nice question. But in production code i would have used paraenthesis for better readability. 😛

Carlo Romagnano SSC-Insane Points: 22596 More actions · Answer 7

palotaiarpad (10/11/2011)
That was a nice question. But in production code i would have used paraenthesis for better readability. 😛

Me, too! 😀

MarkusB SSC-Dedicated Points: 37370 More actions · Answer 8

Very good question even though I missed the point that INTERSECT precedes EXCEPT

[font="Verdana"]Markus Bohse[/font]

Stuart Davies SSCoach Points: 19505 More actions · Answer 9

Good question - thanks.

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BenWard SSCertifiable Points: 5903 More actions · Answer 10

Carlo Romagnano (10/11/2011)
palotaiarpad (10/11/2011)
That was a nice question. But in production code i would have used paraenthesis for better readability. 😛
Me, too! 😀

LOL that would mean that my colleagues could read my code! Can't be having that now can we 🙂

Ben

^ Thats me!

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01010111011010000110000101110100 01100001 0110001101101111011011010111000001101100011001010111010001100101 01110100011010010110110101100101 011101110110000101110011011101000110010101110010
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sqlnaive SSCoach Points: 17437 More actions · Answer 11

Good question.

Thanks vk-kirov for the explanation. However still would like to know the sequential execution of the last query.

call.copse SSCoach Points: 17957 More actions · Answer 12

A very nice question - this is why I continue to do the QOTD. I had honestly never heard of INTERSECT or EXCEPT until today - unbelievable! The precedence totally made sense to me although obviously you would want brackets in real life.

cengland0 SSCertifiable Points: 6102 More actions · Answer 13

vk-kirov (10/10/2011)
Please be aware that the INTERSECT operand has higher precedence than the EXCEPT and UNION operands (http://msdn.microsoft.com/en-us/library/ms188055.aspx):
EXCEPT and INTERSECT (Transact-SQL)
Remarks
If EXCEPT or INTERSECT is used together with other operators in an expression, it is evaluated in the context of the following precedence:
1. Expressions in parentheses
2. The INTERSECT operand
3. EXCEPT and UNION evaluated from left to right based on their position in the expression
So, the code given in the QOTD is equal to the following pseudocode:
( (1, 2, 5)
union
(1, 2, 4) )
except
( (1, 2, 5)
intersect
(1, 2, 4) )
Which is equal to the following pseudocode:
(1, 2, 4, 5)
except
(1, 2)
Which gives us "4, 5" as a result.

Ah, thank you. I too selected just 4 because I didn't know there was a precedence in them and that was not described in the explanation. Makes sense how it works now. Thanks.