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https://issues.apache.org/jira/browse/CALCITE-2421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16550032#comment-16550032
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Jesus Camacho Rodriguez commented on CALCITE-2421:
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[~laurentgo], I did not mean to say that we should fix it as part of this
issue, it was just a general comment within the context of the issue.
[~julianhyde], I think having the 3-case version would be great, the 2-case
version could just be an intermediate step and also help us to clean the code
in the shorter term.
> RexSimplify#simplifyAnds foregoes some simplications if unknownAsFalse set to
> true
> ----------------------------------------------------------------------------------
>
> Key: CALCITE-2421
> URL: https://issues.apache.org/jira/browse/CALCITE-2421
> Project: Calcite
> Issue Type: Bug
> Reporter: Laurent Goujon
> Assignee: Laurent Goujon
> Priority: Minor
>
> It looks like {{RexSimplify#simplifyAnds}} foregoes some comparison
> simplifications if {{unknownAsFalse}} is set to true, like {{A = A AND B =
> B}} which might be simplified to {{A IS NOT NULL AND B IS NOT NULL}} or even
> {{true}} if {{A}} and {{B}} are known to be not nullable.
> One consequence of this is that the selectivity value might be off as a {{=}}
> comparison has a selectivity of 15% whereas {{IS NOT NULL}} has a selectivity
> of 90%.
> The simplication is skipped because {{RexSimplify#simplifyList}} simplify all
> terms with {{unknownAsFalse}} set to {{false}}, but in
> {{RexSimplify#simplifyAnd2ForUnknownAsFalse}}, there's no attempt at trying
> again to simplify each term.
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