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https://issues.apache.org/jira/browse/CALCITE-2807?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16845293#comment-16845293
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Laurent Goujon commented on CALCITE-2807:
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I was not necessary thinking of Github guidelines but guidelines outline in the
git documentation
(https://git-scm.com/book/en/v2/Distributed-Git-Contributing-to-a-Project in
section Commit Guidelines), which is kind of captured by
https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html. Looks
like Linux Kernel development is happy with a summary line with more than 50
characters (but less than 70-75). Calcite guidelines just mention "The first
line of the commit message must be a concise and useful description of the
change."
Not really surprise by Linus' comments regarding Github UI (I have my own beef
with some of the UI choices too).
> Identify expanded IS NOT DISTINCT FROM expression when pushing down filter
> past join
> ------------------------------------------------------------------------------------
>
> Key: CALCITE-2807
> URL: https://issues.apache.org/jira/browse/CALCITE-2807
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Laurent Goujon
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> IS NOT DISTINCT FROM expressions in join condition might actually be
> considered as equi-join conditions, and RelOptUtil#splitJoinConditions() has
> support for it. But some other join related functions/rules don't.
> One of them is RelOptUtil#pushDownJoinConditions (used by
> JoinPushExpressionsRule) which tries to push filter expressions below the
> join, but ends up modifying the join expression in a way which makes identify
> an IDNF condition impossible later.
> For example expression OR(AND(IS_NULL($1), IS_NULL($4)), EQUALS($1,$4)) will
> be changed into OR(AND($3, $6), EQUALS($1, $5)) which makes it
> harder/impossible for RelOptUtil#splitJoinConditions() to identify an IS NOT
> DISTINCT FROM equi-join condition.
> This is a variant of CALCITE-2803
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