andygrove commented on PR #25783:
URL: https://github.com/apache/datafusion/pull/25783#issuecomment-6128353267
Thanks @hsiang-c for tracking this down and for the clear write-up.
Since this PR was opened, #25786 has merged. It makes
`AggregateExec::try_new` return an internal error when there are no grouping
expressions and no aggregate expressions, as suggested above. This matches the
logical `Aggregate`, which has rejected this shape since #3286 and suggests a
single-row `VALUES` instead. With this branch applied to current main, the new
test fails while building the plan:
```
Error: Internal("Grouping expressions and aggregate expressions cannot both
be empty")
```
Since this plan can no longer be built, I think we should close this PR and
#25782, and handle the shape in Comet. apache/datafusion-comet#6899 plans it as
`count(1)` under a `ProjectionExec` with no expressions. I checked that this
returns one row with no columns on current main, for input with rows, empty
input, and zero-column input.
If you still think DataFusion should accept this shape, that means reverting
the check from #25786, so let's discuss it on #25782 first.
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