dd-annarose opened a new pull request, #25337:
URL: https://github.com/apache/datafusion/pull/25337
## Which issue does this PR close?
- Closes #24337.
## Rationale for this change
When using a projection as the percentile argument to
`approx_percentile_cont` or `percentile_cont`, planning fails because only
literals are supported.
It makes sense to accept projections that are constant across all batches
but not labelled as literals (although they practically are).
For example, this query cannot be planned, even though the percentile is
constant:
```
SELECT
approx_percentile_cont(y, m) AS median
FROM (
SELECT t.x + 1 as y, 0.5 as m
FROM (
VALUES (10)
) AS t(x)
)
```
## What changes are included in this PR?
<!--
There is no need to duplicate the description in the issue here, but it is
sometimes worth providing a summary of the individual changes in this PR.
-->
Introduce `PercentileParam` and `PercentileParamState` to handle column
references or projections for the percentile argument.
Resolution of `percentile` cannot always be done: for example, on an empty
record batch, we won't be able to get the value from the columns.
`PercentileParamState` makes sure the percentile resolution is both flexible
enough to wait to be able to resolve the parameter AND applies the strict
constraints that are required (constant `Float32` or `Float64`).
The percentile is also included in state fields so that the merge_batch in
the final Accumulator can process without any issues.
## What is the testing strategy for this PR?
This new feature is covered by the `sqllogictest` cases added in
`aggregate.slt`.
Unit tests have also been added to `approx_percentile_cont.rs` and
`percentile_cont.rs`.
## Are there any user-facing changes?
No breaking changes.
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