yonatan-sevenai opened a new pull request, #21491:
URL: https://github.com/apache/datafusion/pull/21491
## Which issue does this PR close?
- Closes #21490.
## Rationale for this change
When `plan_to_sql` encounters a `Projection → Sort → Projection →
SubqueryAlias` plan where the outer Projection excludes a Sort
column defined as an alias in the inner Projection (e.g. `Z AS c`), the
function `rewrite_plan_for_sort_on_non_projected_fields`
flattens the two Projections into one but only keeps the outer
Projection's columns. This drops the alias definition, leaving
`ORDER BY c` referencing a column that no longer exists in the generated
SQL.
## What changes are included in this PR?
In `rewrite_plan_for_sort_on_non_projected_fields`
(`datafusion/sql/src/unparser/rewrite.rs`), when the inner Projection is
trimmed to only the outer Projection's expressions, sort expressions that
reference dropped aliases are now inlined to the
underlying physical expression. For example, `ORDER BY c` becomes `ORDER
BY t."Z"` when `c` was defined as `Z AS c` in the
dropped inner Projection.
## Are these changes tested?
Yes. A new regression test
`test_sort_on_aliased_column_dropped_by_outer_projection` in
`datafusion/sql/tests/cases/plan_to_sql.rs` constructs the exact plan
shape that triggers the bug and asserts the correct SQL
output:
```sql
SELECT t."X" AS a, t."Y" AS b FROM phys_table AS t ORDER BY t."Z" DESC
NULLS FIRST LIMIT 1
```
All existing `plan_to_sql` tests (118 tests) continue to pass.
## Are there any user-facing changes?
No API changes. Previously invalid SQL is now generated correctly.
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