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https://issues.apache.org/jira/browse/TAJO-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14090507#comment-14090507
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ASF GitHub Bot commented on TAJO-895:
-------------------------------------
GitHub user hyunsik opened a pull request:
https://github.com/apache/tajo/pull/111
TAJO-895: ConstEval should not be included in target list of projectable...
... nodes.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hyunsik/tajo TAJO-895
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/tajo/pull/111.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #111
----
commit f9f90e570abfb31e0139c96d15da0b8f0f042339
Author: Hyunsik Choi <[email protected]>
Date: 2014-08-08T09:13:49Z
TAJO-895: ConstEval should not be included in target list of projectable
nodes.
----
> ConstEval should not be included in target list of projectable nodes
> --------------------------------------------------------------------
>
> Key: TAJO-895
> URL: https://issues.apache.org/jira/browse/TAJO-895
> Project: Tajo
> Issue Type: Improvement
> Components: planner/optimizer
> Reporter: Hyunsik Choi
> Assignee: Hyunsik Choi
> Fix For: 0.9.0
>
>
> In some applications, aliased constant values can be used in WHERE, GROUP BY,
> HAVING, ORDER BY clauses. For those cases, current planner evaluates constant
> value in target list of projectable nodes.
> {code}
> SELECT '1994' end as year, ... FROM lineitem WHERE group by year;
> {code}
> This approach works well so far, but there are rooms for significant
> improvement.
> The main problem is that constant target requires many workaround code in
> NamedExprManager, and TargetListManager. As a result, it makes code
> complexity higher. The second problem is that many constant values evaluated
> in each row consume unnecessary I/O and network bandwidth for storing and
> transmitting.
> The solution seems to be simple. In logical planning phase, we should rewrite
> column references which actually indicates constant values.
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