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https://issues.apache.org/jira/browse/HIVE-1586?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901677#action_12901677
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John Sichi commented on HIVE-1586:
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Predicate pushdown already takes us half-way there, since we end up with this
in the plan:
Filter Operator
predicate:
expr: ('T1' = 'T2')
The remaining work is to evaluate all-constant predicates and if false, replace
the corresponding Filter with a dummy empty input (or propagate the emptiness
further via relational algebra "zero" rules).
> prune operators for empty inputs
> --------------------------------
>
> Key: HIVE-1586
> URL: https://issues.apache.org/jira/browse/HIVE-1586
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Affects Versions: 0.6.0
> Reporter: John Sichi
> Assignee: John Sichi
> Fix For: 0.7.0
>
>
> Given this:
> create view v as
> select * from (
> select *,'T1' as m from pokes
> union all
> select *,'T2' as m from pokes2) u;
> select * from v
> where m='T2';
> When we optimize the query, we can prune away all inputs to the union other
> than the one which references pokes2.
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