[jira] [Commented] (CALCITE-2838) Simplification: Remove redundant IS TRUE checks

["Julian Hyde (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-2838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16765268#comment-16765268 ] 

Julian Hyde commented on CALCITE-2838:
--------------------------------------

I agree that {{x IS TRUE}} is redundant in unknown-as-false mode. However, if {{x}} is nullable the {{IS TRUE}} still useful - it indicates that three-valued logic is being forced into two-valued logic. So, I'd be inclined to keep it, or, in fact, try to push down the {{IS TRUE}} so that the expression becomes two-valued logic throughout.

> Simplification: Remove redundant IS TRUE checks
> -----------------------------------------------
>
>                 Key: CALCITE-2838
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2838
>             Project: Calcite
>          Issue Type: Improvement
>            Reporter: Zoltan Haindrich
>            Assignee: Zoltan Haindrich
>            Priority: Major
>
> In case simplifcation is already processing in unknownAsFalse mode, {{expr IS TRUE}} is redundant - and may just prevent further optimizations from happening:
> {code}
>   @Test public void testRedundantIsTrue() {
>     // in case of unknownAsFalse
>     // x is TRUE <=> x
>     checkSimplify3(isTrue(vBool(1)),
>         "IS TRUE(?0.bool1)",
>         "?0.bool1",
>         "IS TRUE(?0.bool1)");
>   }
> {code}
> there are some further possibilities
> {code}
> (unknownAsTrue) x is NOT FALSE <=> x
> (unknownAsTrue) x is FALSE <=> not x
> {code}



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