[GitHub] [druid] clintropolis commented on pull request #13803: nested columns + arrays = array columns!

["clintropolis (via GitHub)" <gi...@apache.org>]

clintropolis commented on PR #13803:
URL: https://github.com/apache/druid/pull/13803#issuecomment-1481862585

   I've fixed the behavior of `UNNEST` with regards to how it handles `null` and `[]` values for `ARRAY` typed inputs. Per experiments with postgres, `null` and empty arrays `[]` are supposed to output nothing when fed into `UNNEST`:
   
   <img width="1259" alt="Screenshot 2023-03-23 at 2 02 11 AM" src="https://user-images.githubusercontent.com/1577461/227349056-a3d6794c-dcba-4222-86ea-ecd9ceec65f5.png">
   
   <img width="1015" alt="Screenshot 2023-03-23 at 2 04 02 AM" src="https://user-images.githubusercontent.com/1577461/227349099-04e9c280-7ff4-4388-9e37-0708dad62cf4.png">
   
   <img width="1270" alt="Screenshot 2023-03-23 at 2 04 57 AM" src="https://user-images.githubusercontent.com/1577461/227349136-a7b5a2d5-ce81-4ef4-bfb2-42d6bb552687.png">
   
    but currently we are treating them as `[null]`, which is probably unfortunately what we have to keep doing for multi-value `STRING` types because we have trouble distinguishing `null`, `[]` and `[null]`, but no need to do this with actual arrays. So, I have fixed `UnnestColumnValueSelectorCursor` to consume `null` and `[]` values, fixing the behavior and added some tests.
   
   


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