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Posted to issues@hive.apache.org by "Jesus Camacho Rodriguez (JIRA)" <ji...@apache.org> on 2017/06/22 09:15:00 UTC
[jira] [Comment Edited] (HIVE-16934) Transform COUNT(x) into
COUNT() when x is not nullable
[ https://issues.apache.org/jira/browse/HIVE-16934?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16059024#comment-16059024 ]
Jesus Camacho Rodriguez edited comment on HIVE-16934 at 6/22/17 9:14 AM:
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[~vgarg], there are multiple benefits that I can think of. First, at the execution side we will not have to access/evaluate any expression when calculating the COUNT. Further, by removing expressions that are referenced by the aggregate call, we might be able to further prune columns in the operator plan. Another benefit is that this might lead to some aggregate calls not being computed twice, e.g., {{COUNT\(x\)}} and {{COUNT\(y\)}} if _x_ and _y_ are not nullable. Finally, as a side effect, we might be able to recognize more equivalent expressions in MVs rewriting or SharedWorkOptimizer, and push more computation to Druid, since currently Druid is only capable of executing {{COUNT\(*\)}}.
was (Author: jcamachorodriguez):
[~vgarg], there are multiple benefits that I can think of. First, at the execution side we will not have to access/evaluate any expression when calculating the COUNT. Further, by removing expressions that are referenced by the aggregate call, we might be able to further prune columns in the operator plan. Another benefit is that this might lead to some aggregate calls not being computed twice, e.g., {{COUNT(x)}} and {{COUNT(y)}} if _x_ and _y_ are not nullable. Finally, as a side effect, we might be able to recognize more equivalent expressions in MVs rewriting or SharedWorkOptimizer, and push more computation to Druid, since currently Druid is only capable of executing {{count(*)}}.
> Transform COUNT(x) into COUNT() when x is not nullable
> ------------------------------------------------------
>
> Key: HIVE-16934
> URL: https://issues.apache.org/jira/browse/HIVE-16934
> Project: Hive
> Issue Type: Improvement
> Components: Logical Optimizer
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
> Attachments: HIVE-16934.patch
>
>
> Add a rule to simplify COUNT aggregation function if possible, removing expressions that cannot be nullable from its parameters.
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