Prevent empty grouping sets from being eliminated on empty input#22039
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xiedeyantu wants to merge 2 commits intoapache:mainfrom
Open
Prevent empty grouping sets from being eliminated on empty input#22039xiedeyantu wants to merge 2 commits intoapache:mainfrom
xiedeyantu wants to merge 2 commits intoapache:mainfrom
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kosiew
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May 7, 2026
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@xiedeyantu
Thanks for working on this.
Everything looks good overall. I just had one small suggestion around extending the test coverage a bit further.
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| # grouping_sets_empty_input: GROUPING SETS (()) must produce one NULL row on empty input |
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Nice addition to cover explicit GROUPING SETS(()). Since the optimizer change also protects ROLLUP and CUBE through has_empty_grouping_set, it would be great to add small empty-input regression cases for ROLLUP(v1) and CUBE(v1) as well. That would help lock in the full invariant covered by this change.
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Thanks for your review! I added tests for CUBE and ROLLUP.
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Which issue does this PR close?
Rationale for this change
GROUPING SETS (())should return one row even when the input is empty, because the empty grouping set represents a global aggregate. In the current behavior, queries such asWHERE false GROUP BY GROUPING SETS(())can incorrectly be optimized into an empty result, returning 0 rows instead of the expected 1 row. This change fixes that SQL semantics bug.What changes are included in this PR?
This PR makes two related fixes:
It also adds regression coverage in
grouping.sltfor:GROUPING SETS (())on empty inputCOUNT(*)on empty inputAre these changes tested?
Yes. I ran:
cargo test -p datafusion-sqllogictest -- groupingcargo clippy --tests --all-features -p datafusion-physical-plan -p datafusion-optimizer -- -D warningscargo fmt --checkAre there any user-facing changes?
Yes. Queries using
GROUPING SETS (()), and other grouping-set forms that include the empty set such asROLLUPandCUBE, will now return the correct row on empty input instead of incorrectly returning no rows.