[ARROW-6386] [C++][Documentation] Explicit documentation of null slot interpretation

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Resolved
• Fix Version/s: 0.16.0
• Component/s: C++, Documentation
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/22759
• Assignee: Ben Kietzman
• Reporter: Ben Kietzman
• Created: 29/Aug/19 13:36
• Updated: 11/Jan/23 07:46
• Resolved: 14/Jan/20 17:00

Description

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.

Issue Links

• is fixed by: ARROW-6396 [C++] Add ResolveNullOptions to Logical kernels
• links to: GitHub Pull Request #5231