Re: [HACKERS] Idea on how to simplify comparing two sets

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От Pantelis Theodosiou
Тема Re: [HACKERS] Idea on how to simplify comparing two sets
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Msg-id CAE3TBxxPpDuZFp+MGkzbfZcS1+__7Lhi2Z9Dct7p9MDqg9DQHg@mail.gmail.com
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Ответ на Re: [HACKERS] Idea on how to simplify comparing two sets  (Tom Lane <tgl@sss.pgh.pa.us>)
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On Tue, Feb 7, 2017 at 3:58 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Joel Jacobson <joel@trustly.com> writes:
> Currently there is no simple way to check if two sets are equal.

Uh ... maybe check whether SELECT set1 EXCEPT SELECT set2
and SELECT set2 EXCEPT SELECT set1 are both empty?

                        regards, tom lane


Yes, if the wanted result is true or false, something like this:

SELECT EXISTS (TABLE a EXCEPT TABLE b)   OR EXISTS (TABLE b EXCEPT TABLE a) ;

And if a new operator was added (in the same category as UNION and EXCEPT), it could be:


SELECT EXISTS (TABLE a XORSET TABLE b) ;

What about using the = and <> operators in sets? Is the following allowed in the standard?


SELECT (TABLE a) <> (TABLE b) ;

 

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