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Posted to issues@calcite.apache.org by "Julian Hyde (Jira)" <ji...@apache.org> on 2021/02/04 18:23:00 UTC

[jira] [Commented] (CALCITE-4446) Implement three-valued logic for SEARCH operator

    [ https://issues.apache.org/jira/browse/CALCITE-4446?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17279029#comment-17279029 ] 

Julian Hyde commented on CALCITE-4446:
--------------------------------------

Work in progress: [julianhyde/4446-sarg-unknown|https://github.com/julianhyde/calcite/tree/4446-sarg-unknown].

> Implement three-valued logic for SEARCH operator 
> -------------------------------------------------
>
>                 Key: CALCITE-4446
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4446
>             Project: Calcite
>          Issue Type: Bug
>            Reporter: Julian Hyde
>            Priority: Blocker
>             Fix For: 1.27.0
>
>
> Implement three-valued logic for SEARCH operator.
> Consider the expression {{x IN (10, 20)}}, which we might represent as {{SEARCH(x, Sarg(10, 20))}}. Suppose we invoke this with a value of {{NULL}} for {{x}}. Do we want it to return UNKNOWN, FALSE or TRUE? The answer is: all of the above.
> Here are the 3 variants:
> * {{Sarg(10, 20, UNKNOWN AS TRUE)}}: {{x IS NULL OR x IN (10, 20)}} &rarr; TRUE
> * {{Sarg(10, 20, UNKNOWN AS UNKNOWN)}}: {{x IN (10, 20)}} &rarr; UNKNOWN
> * {{Sarg(10, 20, UNKNOWN AS FALSE)}}: {{x IS NOT NULL AND (x IN (10, 20))}} &rarr; FALSE
> Currently {{class Sarg}} has a field {{boolean containsNull}} which deals with the first two cases. Changing {{boolean containsNull}} to {{RexUnknownAs unknownAs}} (which has 3 values) will allow us to represent the third. The new representation is symmetrical under negation, which de Morgan's law suggests is a good thing.



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