[jira] [Assigned] (TAJO-895) ConstEval should not be included in target list of projectable nodes

["Hyunsik Choi (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/TAJO-895?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hyunsik Choi reassigned TAJO-895:
---------------------------------

    Assignee: Hyunsik Choi

> 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
>
> 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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