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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