Union results

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Union results

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Chris Tunstead Grasshopper Points: 21 More actions · Answer 1

Good question, highlighting that union doesn't simply remove a duplicated row where the duplicate exists on both sides of the union, but will also remove a duplicated row where the duplicate rows exist on one side of the union.

Trey Staker SSCarpal Tunnel Points: 4796 More actions · Answer 2

.Thanks for the question

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Paul White SSC Guru Points: 150467 More actions · Answer 3

Cliff Jones (9/22/2011)
Yes, I saw 1,2,3 and almost forgot to count the null value. Good straight forward question with all the likely wrong answers.

I did forget to count the NULL 🙁

Paul White
SQLPerformance.com
SQLkiwi blog
@SQL_Kiwi

Gatekeeper SSCommitted Points: 1633 More actions · Answer 4

SQL Kiwi (9/22/2011)
Cliff Jones (9/22/2011)
Yes, I saw 1,2,3 and almost forgot to count the null value. Good straight forward question with all the likely wrong answers.
I did forget to count the NULL 🙁

This makes me feel much better. Thanks for being honest 😀

/* Anything is possible but is it worth it? */

SQLRNNR SSC Guru Points: 281334 More actions · Answer 5

SQL Kiwi (9/22/2011)
Cliff Jones (9/22/2011)
Yes, I saw 1,2,3 and almost forgot to count the null value. Good straight forward question with all the likely wrong answers.
I did forget to count the NULL 🙁

I nearly missed the null. I glanced over it and then rechecked just before submitting.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
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CoolCodeShare SSCrazy Points: 2584 More actions · Answer 6

CoolCodeShare

SSCrazy

Points: 2584

September 22, 2011 at 9:48 pm

#1385520

Interesting question!!

Thanks.

Koen Verbeeck SSC Guru Points: 259085 More actions · Answer 7

Easy question, thanks.

Need an answer? No, you need a question
My blog at https://sqlkover.com.
MCSE Business Intelligence - Microsoft Data Platform MVP

TomThomson SSC Guru Points: 104773 More actions · Answer 8

Good question.

I nearly counted NULL twice, but remembered in time that the deduplicate operation uses the version of "=" that makes NULL = NULL true.

Tom

Ken SSCoach Points: 17191 More actions · Answer 9

Ken

SSCoach

Points: 17191

September 23, 2011 at 9:19 am

#1385838

Nice question, thanks!

Jason Whitish SSChasing Mays Points: 642 More actions · Answer 10

I found it interesting that the execution plan for the union in the question was the same as if I had done a distinct from the union all

select distinct a from

(select a from a

union all

select a from a) b

In both cases, it did a Concatenation of the two result sets then did a Distinct Sort.

It makes perfect sense that this is how the process would work, once I looked at it, but I thought it was interesting regardless.

I'm pretty easily amused though. :w00t:

Hardy21 SSCrazy Eights Points: 9708 More actions · Answer 11

Hardy21

SSCrazy Eights

Points: 9708

September 26, 2011 at 10:09 pm

#1386912

Easy & Straight forward question..

Thanks

spaghettidba SSC Guru Points: 105732 More actions · Answer 12

SQL Kiwi (9/22/2011)
Cliff Jones (9/22/2011)
Yes, I saw 1,2,3 and almost forgot to count the null value. Good straight forward question with all the likely wrong answers.
I did forget to count the NULL 🙁

+1

I didn't see it at all. My bad.

-- Gianluca Sartori

terrykzncs Ten Centuries Points: 1324 More actions · Answer 13

Good question.

I didn't realize that the union would affect the first table as well. Was expecting both of the 1's to still be intact and therefore give 5 instead of 4......