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https://issues.apache.org/jira/browse/CALCITE-2632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16699068#comment-16699068
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Zoltan Haindrich commented on CALCITE-2632:
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I was looking into how to fix an issue; and I've just [noticed this issue
again|https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L670]...
I think this more important...than it looks like...
> Add hashCode and equals implementations to RexNode
> ---------------------------------------------------
>
> Key: CALCITE-2632
> URL: https://issues.apache.org/jira/browse/CALCITE-2632
> Project: Calcite
> Issue Type: Bug
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
>
> Right now RexNode doesn't have any equals or hashCode functions; which makes
> it rely on the default implementation.
> But when we are writing simplification logics we sometimes forget to use
> {{toString()}} during comparisions and may try to rely on pure equals:
> * there is a [Set of
> RexNode-s|https://github.com/apache/calcite/blob/5b16e23dff03e5eaed80642ae91e28ebf806e6b0/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L1104]
> during {{AND}} simplification and in [RexUtil as
> well|https://github.com/apache/calcite/blob/5b16e23dff03e5eaed80642ae91e28ebf806e6b0/core/src/main/java/org/apache/calcite/rex/RexUtil.java#L321]
> * I've by mistake just written rexNode.equals(otherRexNode) during the
> implementation of CALCITE-1413
> * I've just bumped into the same thing...that
> [RexUtil.andNot|https://github.com/apache/calcite/blob/5b16e23dff03e5eaed80642ae91e28ebf806e6b0/core/src/main/java/org/apache/calcite/rex/RexUtil.java#L1888]
> is also rely on it....and I think those comparisions go back a while
> (~3years at least) ; and a bug is not appeared from it because this
> comparision is in most cases false.
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