Re: Selecting K random rows - efficiently! - Mailing list pgsql-general

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Subject Re: Selecting K random rows - efficiently!
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Msg-id ffnid8$1q2t$1@news.hub.org
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In response to Re: Selecting K random rows - efficiently!  (Martijn van Oosterhout <kleptog@svana.org>)
List pgsql-general
> How important is true randomness?

The goal is an even distribution but currently I have not seen any way
to produce any kind of random sampling efficiently. Notice the word
"efficiently". The naive way of taking a random sample of size K:
    (SELECT * FROM mydata ORDER BY random() LIMIT <K>)
is clearly not an option for performance reasons. It shouldn't be
necessary to explain why. :-)

> Search the archives, there have been solutions proposed before, though
> they probably arn't very quick...

As the subject suggests, performance really matters and searching the
archives only results in poor solutions (my first post explains why).

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