mustafasrepo opened a new pull request, #8327:
URL: https://github.com/apache/arrow-datafusion/pull/8327
## Which issue does this PR close?
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Closes #.
## Rationale for this change
Currently we cannot calculate `NTH_VALUE` result in reverse order. However,
this can be done, if we were to support negative index for `NTH_VALUE` (as in
python arrays). With this support we can calculate reverse representation of
`NTH_VALUE` to better optimize some plans. Please note that negative index
cannot be entered from the SQL query. In this sense, there is no difference
from the user point of view.
However, query below
```sql
SELECT c, NTH_VALUE(c, 2) OVER(order by c DESC RANGE BETWEEN UNBOUNDED
PRECEDING AND CURRENT ROW) as nv1
FROM multiple_ordered_table
ORDER BY c ASC
LIMIT 5
```
where `multiple_ordered_table` satisfied `c ASC` ordering, is re-written as
the following behind the scenes
```
SELECT c, NTH_VALUE(c, -2) OVER(order by c ASC RANGE BETWEEN CURRENT ROW and
UNBOUNDED FOLLOWING) as nv1
FROM multiple_ordered_table
ORDER BY c ASC
LIMIT 5
```
which can be executed without introducing any `SortExec` to the plan.
For window frame reversal see `Constructing Equivalent Window Frames for
Reverse Expressions` section in the [blog
post](https://www.synnada.ai/blog/running-window-query-in-stream-processing).
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## What changes are included in this PR?
This PR add negative index support to the `NTH_VALUE` window function to
support reverse order execution.
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## Are these changes tested?
Yes.
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## Are there any user-facing changes?
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