Logical Operators

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Logical Operators

Robin Sasson

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May 23, 2012 at 10:45 pm

#258620

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May 24, 2012 at 3:30 am

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Koen Verbeeck SSC Guru Points: 259105 More actions · Answer 1

Nice question, thanks.

Need an answer? No, you need a question
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TomThomson SSC Guru Points: 104773 More actions · Answer 2

TomThomson

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May 24, 2012 at 3:24 am

#1492342

Nice easy one today.

Tom

kapfundestanley SSCertifiable Points: 5637 More actions · Answer 3

Very easy question,thank you for the point.

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sanjeewan99 Say Hey Kid Points: 700 More actions · Answer 4

sanjeewan99

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May 24, 2012 at 3:48 am

#1492359

Nice Easy question thanks

Toreador SSChampion Points: 11365 More actions · Answer 5

I can't believe that 21% have currently got it completely wrong, thinking that OR has precedence over AND! Hopefully they're just all misunderstanding what 'precedence' means 😉

DugyC Hall of Fame Points: 3804 More actions · Answer 6

Basic computer science question, nice and easy, thanks.

Can't believe almost a third got it wrong!

Bak to skool! 😛

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rfr.ferrari SSCertifiable Points: 6879 More actions · Answer 7

nice question!!!

back to basic!!!!

Thanks!!

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TomThomson SSC Guru Points: 104773 More actions · Answer 8

Toreador (5/24/2012)
I can't believe that 21% have currently got it completely wrong, thinking that OR has precedence over AND! Hopefully they're just all misunderstanding what 'precedence' means 😉

It seems more likely that they've misunderstood what MicroSoft means by "higher" on the BoL Page Operator Precedence. The question is sensibly phrased, using "has precedence over". The BoL page says "An operator on higher levels is evaluated before an operator on a lower level", and then provides a table with AND on level 6 and OR on level 7. It would not be unreasonable for people to think that level 7 is a higher level than level 6, and perhaps that accounts for the 21% very wrong answers. But level 7 is lower than level 6, as anyone who looks at the page layout (the right way up) can tell :w00t:.

On that BoL page, a "higher" level is the one introduced closer to the top of the page, not one with a higher level number. Since the table is printed starting with level 1 at the top and continues in nummerical order of level number, the "higher level" is always the level with the lower number.

The various BoL pages on this topic from SQL 2000 onwards have all misused "higher" in this sense; it was pointed out to MS about 12 years ago, but they think it's OK :crazy:. Perhaps they speak a different English in Redmond. 😉

Edit: it is of course to be hoped that none of the people thinking OR has precedence over AND has ever written any T-SQL that depends on that misunderstanding - or if they have, that they wrote it so recently that they haven't yet done any unit testing!

Tom

TomThomson SSC Guru Points: 104773 More actions · Answer 9

DugyC (5/24/2012)
Basic computer science question, nice and easy, thanks.
Can't believe almost a third got it wrong!
Bak to skool! 😛

"computer science" question? Since when was T-SQL operator precedence part of computer science? Do you think that all computer languages give AND precedence over OR? If so you will be surprised when you come across languages that give OR precedence over AND, languages that have left to right precedence, languages that have right to left precedence, and languages where not fixing evaluation order by overt syntactic means (using brackets or dots) is a syntax error.

It is indeed surprising that so many got it wrong, though. I suspect it's MS's fault (see earlier post).

Tom

Robin Sasson Hall of Fame Points: 3359 More actions · Answer 10

L' Eomot Inversé, you make a fair point. BOL could do with some improving in this respect.

Thank you all for you comments - much appreciated!

:exclamation: "Be brave. Take risks. Nothing can substitute experience." :exclamation:

ronmoses@gmail.com SSCarpal Tunnel Points: 4480 More actions · Answer 11

The only reason I had to think about it a while is that I would never combine AND and OR without parentheses, so that fact was a bit dusty in my brain. Yeah, it's something you should know, but it should also be something you don't have to worry about.

ron

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Igor Micev SSC-Dedicated Points: 33109 More actions · Answer 12

A good question

But,

"Which of the following facts are correct when constructing a WHERE clause with no parenthesis?" ?

Not all the statements are facts, only one is - "AND has precedence over OR".

Thanks

IgorMi

Igor Micev,My blog: www.igormicev.com

paul.knibbs SSCoach Points: 15320 More actions · Answer 13

This is something I pretty much never bother to remember, because if there's any ambiguity I always add parentheses...makes it easier for humans to understand that way.