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https://issues.apache.org/jira/browse/CALCITE-2582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16622345#comment-16622345
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Julian Hyde commented on CALCITE-2582:
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I believe that in all of the cases that changed in sub-query.iq show that the
original expression was not simplified. So the question is, which code created
them, and why did it not simplify?
Given the same expression and the same input fields, the simplifier can only do
a better job if it has more predicates. And that is not the case when pushing a
filter through a project. The input has the same predicates, I believe.
> FilterProjectTransposeRule does not always simplify the new filter condition
> ----------------------------------------------------------------------------
>
> Key: CALCITE-2582
> URL: https://issues.apache.org/jira/browse/CALCITE-2582
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.17.0
> Reporter: Stamatis Zampetakis
> Assignee: Julian Hyde
> Priority: Minor
> Fix For: 1.18.0
>
>
> After pushing the filter below the project a new condition is going to be
> generated along with a new Filter operator. The new condition is not going to
> be simplified if the filter operator is copied and not created using the
> RelBuilder.
> Thus the resulting plan may contain redundant conditions which can have a
> slight impact on performance. Apart, from that tests verifying the resulting
> (logical/physical) plan may produce indeterministic results if the rule is
> applied with (a different order and in combination with other rules).
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