hsiang-c opened a new pull request, #25783:
URL: https://github.com/apache/datafusion/pull/25783
## Which issue does this PR close?
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- Closes #25782
## Rationale for this change
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`AggregateStream` finalizes with `RecordBatch::try_new`, which infers the
row count from the first column. A no-grouping aggregate with no aggregate
expressions has neither columns nor a non-empty schema, so Arrow's
`RecordBatch` rejects the batch with "must either specify a row count or at
least one column" instead of emitting the single empty row the plan describes.
A no-grouping aggregate always finalizes to exactly one row, and every
column produced by `finalize_aggregation` is a length-1 array.
`optimize_projections` rewrites this shape into `EmptyRelation {
produce_one_row: true }`, so SQL never reaches it; callers like Comet that
build physical plans directly do.
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## Are there any user-facing changes?
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No
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