[jira] [Created] (ARROW-6386) [C++][Documentation] Explicit documentation of null slot interpretation

["Benjamin Kietzman (Jira)" <ji...@apache.org>]

Benjamin Kietzman created ARROW-6386:
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             Summary: [C++][Documentation] Explicit documentation of null slot interpretation
                 Key: ARROW-6386
                 URL: https://issues.apache.org/jira/browse/ARROW-6386
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++, Documentation
            Reporter: Benjamin Kietzman
            Assignee: Benjamin Kietzman


To my knowledge, there isn't explicit documentation on how null slots in an array should be interpreted. SQL uses Kleene logic, wherein a null is explicitly an unknown rather than a special value. This yields for example `(null AND false) -> false`, since `(x AND false) -> false` for all possible values of x. This is also the behavior of Gandiva's boolean expressions.

By contrast the boolean kernels implement something closer to the behavior of NaN: `(null AND false) -> null`. I think this is simply an error in the boolean kernels but in any case I think explicit documentation should be added to prevent future confusion.





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