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From "John Sichi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-1586) prune operators for empty inputs
Date Tue, 24 Aug 2010 00:04:16 GMT

    [ https://issues.apache.org/jira/browse/HIVE-1586?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901677#action_12901677
] 

John Sichi commented on HIVE-1586:
----------------------------------

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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