[CALCITE-6087] EnumerableSortedAggregate returns incorrect result when input is empty

[1fanwang]

Jira Link

CALCITE-6087

Changes Proposed

When a query applies MAX or COUNT to empty input, a sorted global aggregate returns no row. SQL requires one row containing NULL and 0.

Sorted grouping emits one row per observed key, but a global aggregate has no grouping key. The sorted aggregate rule now declines an empty group set, so EnumerableAggregate handles it through its zero-key singleton path. Grouped sorted aggregates are unchanged.

Testing

Scenario	Result
Forced sorted execution before the fix	Empty result instead of m=null; c=0
Standard aggregate after the fix	m=null; c=0
Sorted-only planning after the fix	Expected planning failure

Raw logs

With the pre-fix parent version of EnumerableSortedAggregateRule:

$ JAVA_HOME=$(/usr/libexec/java_home -v 21) ./gradlew :core:test --tests org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest.sortedAggOnEmptyInput --no-daemon --console=plain
Expected: "m=null; c=0"
     but: was ""
1 test completed, 1 failed
BUILD FAILED

$ JAVA_HOME=$(/usr/libexec/java_home -v 21) ./gradlew :core:test --tests 'org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest.aggOnEmptyInput' --tests 'org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest.sortedAggRuleRejectsEmptyGroupSet' --no-daemon --console=plain --rerun-tasks
Expected: a string containing "There are not enough rules to produce a node with desired properties"
     but: was "org.opentest4j.AssertionFailedError: expected exception but none was thrown"
2 tests completed, 1 failed
BUILD FAILED

With this PR, the standard-path assertion observed m=null; c=0:

$ JAVA_HOME=$(/usr/libexec/java_home -v 21) ./gradlew :core:test --tests 'org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest.aggOnEmptyInput' --tests 'org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest.sortedAggRuleRejectsEmptyGroupSet' --no-daemon --console=plain --rerun-tasks
2 completed, 0 failed, 0 skipped
BUILD SUCCESSFUL

$ JAVA_HOME=$(/usr/libexec/java_home -v 21) ./gradlew :core:test --tests 'org.apache.calcite.test.enumerable.EnumerableSortedAggregateTest' --no-daemon --console=plain
13 completed, 0 failed, 0 skipped
BUILD SUCCESSFUL

[xuzifu666]

Thank you for the contribution! Please take a look to jira discussion.

[rubenada]

Thanks for the contribution @1fanwang !
@xuzifu666 I opened this ticket long time ago, I had a suspicion about a probably fix (implemented in this PR), I asked the contributors that worked on the EnumerableSortedAggregate for their opinion about the fix, but got no answer.
I think we can move forward if we are indeed correcting a bug.

[1fanwang]

Thank you for the contribution! Please take a look to jira discussion.

thanks for the pointer @xuzifu666
I think the direction from CALCITE-6087 is to reject empty groupSets in EnumerableSortedAggregateRule

done in d3b829a

[rubenada]

Thanks @1fanwang , LGTM. I just left some minor comment.
Could you please also squash commits into a single one (keeping [CALCITE-6087] EnumerableSortedAggregate returns incorrect result when input is empty as final commit message)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
80.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[rubenada]

Thanks for the patch @1fanwang !
If you want to continue contributing on this area, there's a related ticket https://issues.apache.org/jira/browse/CALCITE-6089 which may have been also fixed by the current patch. It'd be needed to verify it (and add the appropriate tests, similar to the ones here to prevent any regression in the future).