andygrove opened a new issue, #6476:
URL: https://github.com/apache/datafusion-comet/issues/6476
### Describe the bug
Spark orders a null element of an array key, and a null field of a struct
key, below every other value, whatever the key's `NULLS FIRST` or `NULLS LAST`,
which applies only to a null key itself. Comet's native sort takes the position
of nested nulls from the key's null order instead. With the default null
orders, `ASC NULLS FIRST` and `DESC NULLS LAST`, the two agree, but `ASC NULLS
LAST` and `DESC NULLS FIRST` put a key that holds a null element at the other
end from Spark.
### Steps to reproduce
```sql
CREATE TABLE t(id INT, i INT) USING parquet;
INSERT INTO t VALUES (1, 1), (2, NULL), (3, 3);
SELECT id FROM t ORDER BY array(i) DESC NULLS FIRST, id;
-- Spark: 3, 1, 2 Comet: 2, 3, 1
SELECT id FROM t ORDER BY named_struct('x', i) NULLS LAST, id;
-- Spark: 2, 1, 3 Comet: 1, 3, 2
```
### Expected behavior
A null element or field sorts below every other value, as in Spark, whatever
the key's null order. The same applies to TopK and to window order keys.
### Additional context
Found while fixing #5507 in #6475, whose fixture keeps the default null
orders to stay clear of this.
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