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https://issues.apache.org/jira/browse/HIVE-6873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13965915#comment-13965915
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Jitendra Nath Pandey commented on HIVE-6873:
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Here is a scenario where we get incorrect result. It shows up on sorted
bucketed column with hive.map.groupby.sorted=true, and only on group by queries
with no keys.
Here are the steps:
hive> Create table T(a int, b int) clustered by (a) sorted by (a) stored as orc;
load following data:
300 1
300 1
300 1
300 1
300 1
hive> set hive.map.groupby.sorted=true;
hive> select sum(distinct a) from T; // Incorrect result.
hive> select count(distinct a) from T; // This is also incorrect.
> DISTINCT clause in aggregates is handled incorrectly by vectorized execution
> ----------------------------------------------------------------------------
>
> Key: HIVE-6873
> URL: https://issues.apache.org/jira/browse/HIVE-6873
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.13.0, 0.14.0
> Reporter: Remus Rusanu
> Assignee: Remus Rusanu
> Attachments: HIVE-6873.1.patch, HIVE-6873.2.patch
>
>
> The vectorized aggregates ignore the DISTINCT clause. This cause incorrect
> results. Due to how GroupByOperatorDesc adds the DISTINCT keys to the overall
> aggregate keys the vectorized aggregates do account for the extra key, but
> they do not process the data correctly for the key. the reduce side the
> aggregates the input from the vectorized map side to results that are only
> sometimes correct but mostly incorrect. HIVE-4607 tracks the proper fix, but
> meantime I'm filing a bug to disable vectorized execution if DISTINCT is
> present. Fix is trivial.
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