izveigor opened a new issue, #6995:
URL: https://github.com/apache/arrow-datafusion/issues/6995
### Is your feature request related to a problem or challenge?
## Summary
| Characteristic | Description
|
| --------------------- |
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|
| Function name: | `flatten`
|
| Aliases: | -
|
| Original function?: | No
|
| Function Description: | <b>Azure DataBricks:</b> Returns an array of the
elements in the union of array1 and array2 without duplicates. </br> <b>Spark
SQL:</b> Creates a single array from an array of arrays column. </br>
<b>ClickHouse:</b> Converts an array of arrays to a flat array. Function:
Applies to any depth of nested arrays. Does not change arrays that are already
flat. The flattened array contains all the elements from all source arrays.
</br> <b>DuckDB:</b> Concatenate a list of lists into a single list. This only
flattens one level of the list (see examples). |
| Sources: |
[Concept](https://github.com/apache/arrow-datafusion/discussions/6855)
[Azure](https://learn.microsoft.com/en-us/azure/databricks/sql/language-manual/functions/flatten)
[DuckDB](https://duckdb.org/docs/sql/functions/nested)
[ClickHouse](https://clickhouse.com/docs/en/sql-reference/functions/array-functions#arrayflatten)
[Spark](https://sparkbyexamples.com/spark/spark-sql-array-functions/)
|
## Examples:
```
D select flatten([[1, 2, 3], [4, 5, 6]]);
┌──────────────────────────────────────────────────────────────────────────────┐
│ flatten(main.list_value(main.list_value(1, 2, 3), main.list_value(4, 5,
6))) │
│ int32[]
│
├──────────────────────────────────────────────────────────────────────────────┤
│ [1, 2, 3, 4, 5, 6]
│
└──────────────────────────────────────────────────────────────────────────────┘
D select flatten([[[1, 1], [2, 2], [3, 3]], [[4, 4], [5, 5], [6, 6]]]);
┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ flatten(main.list_value(main.list_value(main.list_value(1, 1),
main.list_value(2, 2), main.list_value(3, 3)),
main.list_value(main.list_value(4, 4), main.li… │
│
int32[][]
│
├────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ [[1, 1], [2, 2], [3, 3], [4, 4], [5, 5], [6, 6]]
│
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
```
### Describe the solution you'd like
_No response_
### Describe alternatives you've considered
_No response_
### Additional context
_No response_
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