kumarUjjawal opened a new pull request, #22169:
URL: https://github.com/apache/datafusion/pull/22169
## Which issue does this PR close?
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- Closes #17256.
## Rationale for this change
DataFusion currently rejects `DISTINCT ON` queries when they are combined
with `GROUP BY`, aggregate functions, or window functions.
PostgreSQL allows these queries. The planner already builds the aggregate
and window plan before applying `DISTINCT ON`, but the old `DISTINCT ON` path
only worked against the pre-aggregation input. That meant expressions that
depended on aggregate or window output could not be planned.
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## What changes are included in this PR?
This PR updates `DISTINCT ON` planning so its expressions participate in the
same aggregate and window rewrite pipeline as `SELECT`, `HAVING`, `QUALIFY`,
and `ORDER BY`.
It also keeps hidden `DISTINCT ON` keys and `ORDER BY` tie-breakers in
scope before the final projection, so valid PostgreSQL-style queries work even
when those expressions are not in the select list.
The change also handles SELECT alias resolution for `DISTINCT ON` and `ORDER
BY` in the PostgreSQL-compatible way: a bare alias can resolve to the select
expression, while the same name inside a larger expression still resolves as an
input column.
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## Are these changes tested?
Yes
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## Are there any user-facing changes?
No public API Change
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