[PR] [SPARK-57775][SQL][4.0] Return one row for GROUP BY GROUPING SETS (()) over empty input [spark]

["uros-b (via GitHub)" <gi...@apache.org>]

uros-b opened a new pull request, #57244:
URL: https://github.com/apache/spark/pull/57244

   ### What changes were proposed in this pull request?
   
   Note: this is a 4.0 backport of https://github.com/apache/spark/pull/56891.
   
   Lower the single-empty-grouping-set case to a global `Aggregate` (no grouping expressions, no `Expand`), so it returns one (grand total) row over empty input, matching the `GROUP BY`-less form and the SQL standard. `grouping_id()` folds to the constant `0`, and `grouping()`/`grouping_id()` in `HAVING`/`ORDER BY` resolve against that constant.
   
   Unlike the master/4.2 change, which lives in `GroupingAnalyticsTransformer` (introduced later by SPARK-54961), branch-4.1 has no such object: the grouping-analytics lowering is still inline in `Analyzer.ResolveGroupingAnalytics`, so the fix is re-implemented there. branch-4.1 also has no single-pass `GroupingAnalyticsResolver` (grouping analytics is not supported by the single-pass resolver on 4.1, guarded out in `ResolverGuard`), so the fix lands only in the legacy fixed-point analyzer.
   
   ### Why are the changes needed?
   
   `GROUP BY GROUPING SETS (())` is a grand total, semantically identical to an aggregation with no `GROUP BY` clause. It was lowered to a grouped `Aggregate` over an `Expand` (grouping by `spark_grouping_id`), so over empty input it returned zero rows instead of one. The same defect affected the equivalent empty `GROUP BY CUBE()` and `GROUP BY ROLLUP()`, which also lower to a single empty grouping set.
   
   ### Does this PR introduce _any_ user-facing change?
   
   Yes, the new (correct) behavior is gated by an internal SQL config,
   `spark.sql.analyzer.lowerEmptyGroupingSetToGlobalAggregate.enabled` (default true). When set to false, lowering reverts to the legacy `Expand`-based form (zero rows over empty input). The flag gates both the transformer lowering and the `grouping_id()` resolution in `HAVING`/`ORDER BY`, so the off state reproduces pre-fix behavior identically.
   
   ### How was this patch tested?
   
   Tested via golden cases in `grouping_set.sql` (empty-input grand total, `grouping_id()` in SELECT/HAVING/ORDER BY, `grouping()` rejection, non-empty input), flag-off coverage in `grouping_set_grand_total_disabled.sql`, `ResolveGroupingAnalyticsSuite`, `DataFrameAggregateSuite`, and the Connect `ClientE2ETestSuite`.
   
   ### Was this patch authored or co-authored using generative AI tooling?
   
   Generated-by: Opus 4.8
   


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Re: [PR] [SPARK-57775][SQL][4.0] Return one row for GROUP BY GROUPING SETS (()) over empty input [spark]

["uros-b (via GitHub)" <gi...@apache.org>]

uros-b closed pull request #57244: [SPARK-57775][SQL][4.0] Return one row for GROUP BY GROUPING SETS (()) over empty input
URL: https://github.com/apache/spark/pull/57244


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Re: [PR] [SPARK-57775][SQL][4.0] Return one row for GROUP BY GROUPING SETS (()) over empty input [spark]

["uros-b (via GitHub)" <gi...@apache.org>]

uros-b commented on PR #57244:
URL: https://github.com/apache/spark/pull/57244#issuecomment-4978950518

   Same as https://github.com/apache/spark/pull/57222#issuecomment-4978947658, closing this backport PR.


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