neilconway opened a new issue, #24981:
URL: https://github.com/apache/datafusion/issues/24981
### Describe the bug
The docs for `map_extract` say that it returns an empty list if the
requested key is not present in the map, but that is not the implemented
behavior: `[NULL]` is returned instead. This behavior does not match how
`map_extract` behaves in DuckDB; it also makes it impossible to distinguish
between an absent key and a key whose associated value is `NULL`, which is
arguably the point of having `map_extract` return a list in the first place.
### To Reproduce
```sql
SELECT
map_extract(MAP {'a': 1, 'b': NULL}, 'a') AS present,
map_extract(MAP {'a': 1, 'b': NULL}, 'b') AS present_null,
map_extract(MAP {'a': 1, 'b': NULL}, 'c') AS missing,
element_at(MAP {'a': 1, 'b': NULL}, 'c') AS alias_missing;
```
Verified using DataFusion CLI 55.0.0 and DuckDB v1.5.5:
| Engine | present | present_null | missing | alias_missing |
|---|---|---|---|---|
| DataFusion | `[1]` | `[NULL]` | `[NULL]` | `[NULL]` |
| DuckDB | `[1]` | `[NULL]` | `[]` | `[]` |
### Expected behavior
`map_extract` should return `[]` for a missing key.
### Additional context
_No response_
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