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

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

Hyunsik Choi created TAJO-895:
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             Summary: 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


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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