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https://issues.apache.org/jira/browse/HIVE-16255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16792824#comment-16792824
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Laszlo Bodor commented on HIVE-16255:
-------------------------------------
discussed with [~kgyrtkirk] again, due to HIVE-21338, the aggregation function
cannot rely on the fact that arriving elements are ordered in an aggregate, so
the original implementation (05.patch) would make do (sorting manually on
terminate)
additionally, I refactored it in 06.patch to eliminate code duplications
(LongWritable/DoubleWritable)
WITHIN GROUP followup is: HIVE-21449
cc: [~ashutoshc], [~mgergely]
> Support percentile_cont / percentile_disc
> -----------------------------------------
>
> Key: HIVE-16255
> URL: https://issues.apache.org/jira/browse/HIVE-16255
> Project: Hive
> Issue Type: Sub-task
> Components: SQL
> Reporter: Carter Shanklin
> Assignee: Laszlo Bodor
> Priority: Major
> Attachments: HIVE-16255.01.patch, HIVE-16255.02.patch,
> HIVE-16255.03.patch, HIVE-16255.04.patch, HIVE-16255.05.patch,
> HIVE-16255.06.patch
>
>
> Way back in HIVE-259, a percentile function was added that provides a subset
> of the standard percentile_cont aggregate function.
> The SQL standard provides some additional options and also a percentile_disc
> aggregate function with different rules. In the standard you specify an
> ordering with arbitrary value expression and the results are drawn from this
> value expression. This aggregate functions should be usable as analytic
> functions as well (i.e. support the over clause). The current percentile
> function is able to be used with an over clause.
> The rough outline of how this works is:
> percentile_cont(number) within group (order by expression) [ over(window
> spec) ]
> percentile_disc(number) within group (order by expression) [ over(window
> spec) ]
> The value of number should be between 0 and 1. The value expression is
> evaluated for each row of the group, nulls are discarded, and the remaining
> rows are ordered.
> — If PERCENTILE_CONT is specified, by considering the pair of consecutive
> rows that are indicated by the argument, treated as a fraction of the total
> number of rows in the group, and interpolating the value of the value
> expression evaluated for these rows.
> — If PERCENTILE_DISC is specified, by treating the group as a window
> partition of the CUME_DIST window function, using the specified ordering of
> the value expression as the window ordering, and returning the first value
> expression whose cumulative distribution value is greater than or equal to
> the argument.
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