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Ted Dunning commented on DRILL-20:
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{quote}
[~gera.shegalov], [~julianhyde] and [~tdunning], do any of you have any
thoughts on whether segment-based limit should be a part of the limit logical
operator?
{quote}
In Dremelish settings, limit itself is rarely used at the top-level because it
generally implies a sort step. The only exception might be debugging where you
just want to see some of the output. Approximate top() is used almost
exclusively for these sorts of situations and it should be supported in segment
and top-level contexts.
That said, I would think it useful to support top-level and per segment limit
as well as top. One use-case that I can imagine is in recommendations where I
would want to retain the first or last records for each user, but do not want
more than, say, 1000 events. The input would already be approximately in
temporal order so limit would be fine. It would be better, even in this case
to use top so I could specify a precise retention criterion such as time or a
random number, but limit should be supported as well.
> Limit Operator Reference Implementation
> ---------------------------------------
>
> Key: DRILL-20
> URL: https://issues.apache.org/jira/browse/DRILL-20
> Project: Apache Drill
> Issue Type: Improvement
> Reporter: Chris Merrick
> Attachments: limit-reference.patch
>
>
> Build off of Jacques work on reference implementations - the limit operator.
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