Fun with XOR #2

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Fun with XOR #2

DonlSimpson

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December 6, 2014 at 12:52 pm

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Comments posted to this topic are about the item Fun with XOR #2
Don Simpson

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December 8, 2014 at 12:43 am

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TomThomson SSC Guru Points: 104773 More actions · Answer 1

The same question (just phrased a little differently) for Monday as we had for Friday seems a bit odd, especially with two points for each one. But it's still a fun question.

It's also still pretty trivial logic, and I find it appalling that 45% (344 out of 771) got it wrong when it was asked on Friday. I hope the number of wrong answers will be lower for the Monday version.

Tom

Hugo Kornelis SSC Guru Points: 64790 More actions · Answer 2

DonlSimpson (12/6/2014)
Comments posted to this topic are about the item <A HREF="/questions/T-SQL/119238/">Fun with XOR #2</A>

There are good use cases for bitwise logic in SQL Server. This is not one of them.

Pretty good trivia question, but readers: please do not ever think about using this in production code.

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TomThomson SSC Guru Points: 104773 More actions · Answer 3

Hugo Kornelis (12/7/2014)
There are good use cases for bitwise logic in SQL Server. This is not one of them.
Pretty good trivia question, but readers: please do not ever think about using this in production code.

Yes, it would indeed be pretty stupid to write

select (@a ^ @b-2) ^ ((@a ^ @b-2) ^ @b-2), (@a ^ @b-2) ^ @b-2

instead of

select @b-2, @a

except perhaps as part of deliberate code obfuscation.

Tom

DonlSimpson SSCertifiable Points: 7043 More actions · Answer 4

Hugo Kornelis (12/7/2014)
There are good use cases for bitwise logic in SQL Server. This is not one of them.
Pretty good trivia question, but readers: please do not ever think about using this in production code.

Perhaps you could read the explanation:

Not the easy way to do anything, but might be good for a computer science class.

I think it was pretty clear that this was not a suggested technique.

Don Simpson

I'm not sure about Heisenberg.

Umer Akram SSC-Insane Points: 22209 More actions · Answer 5

Umer Akram

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December 8, 2014 at 12:15 am

#1763195

Nice question. Thanks for sharing

Koen Verbeeck SSC Guru Points: 259115 More actions · Answer 6

Nice question, thanks.

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dale_berta Ten Centuries Points: 1325 More actions · Answer 7

Actually, I'm wondering if many who got the previous post wrong was because we weren't familiar with the '^' operator. I incorrectly assumed it meant exponentiation.

Granted, not useful in everyday SQL, but the current question is similar to the math behind RAIDed disk. The basic deal is parity is an XOR, P = A^B. If you lose A, then A = P^B = (A^B)^B, and similarly if you lose B.

Xavon SSCrazy Points: 2280 More actions · Answer 8

dale_berta (12/8/2014)
Actually, I'm wondering if many who got the previous post wrong was because we weren't familiar with the '^' operator. I incorrectly assumed it meant exponentiation.

This might be the case. It has always been one of my biggest gripes about SQL Server. Everywhere else in the known universe (hyperbole to illustrate my level of frustration) ^ means exponent. But SQL Server makes it XOR. I can't tell you how many times that messed me up (okay, probably only 3 or 4, but again, hyperbole for point).

Dana Medley SSCertifiable Points: 6764 More actions · Answer 9

Dana Medley

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December 8, 2014 at 7:33 am

#1763275

Thanks for the question.

Everything is awesome!

RK Mandava SSCarpal Tunnel Points: 4153 More actions · Answer 10

Stewart "Arturius" Campbell (12/8/2014)
Interesting question, thanks Don
TomThomson (12/6/2014)
The same question (just phrased a little differently) for Monday as we had for Friday seems a bit odd, especially with two points for each one. But it's still a fun question.
It's also still pretty trivial logic, and I find it appalling that 45% (344 out of 771) got it wrong when it was asked on Friday. I hope the number of wrong answers will be lower for the Monday version.
Agreed.

+1

SQLRNNR SSC Guru Points: 281334 More actions · Answer 11

Thanks Don. Fun question.

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Ed Wagner SSC Guru Points: 287026 More actions · Answer 12

Nice question. I also agree with Tom that 45% is pretty dismal. Knowing the basics is never a bad thing. The more you understand old techniques and how things work under the hood, the better you are at coming up with good and high-performance solutions to current problems.

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robolance SSC-Addicted Points: 403 More actions · Answer 13

I was unhappy with the whole question because I was sure I got the math right. Then I read some of the other comments and realized that ^ means something other than exponent. That is why I still do these each day, sometimes I get exposed to new theories and thoughts, Sometimes it just little things. But, sometimes the little things trip you up and I learned something almost trivial. Trivial until it shows up in someones SQL and you are trying to fix.

Thanks