[CALCITE-7757] RelMdFunctionalDependency can infer unsound dependencies and cause incorrect query results

[darpan-14]

Jira Link

CALCITE-7757

Changes Proposed

RelMdFunctionalDependency can currently expose unsound or incorrectly indexed dependencies, allowing AggregateRemoveDuplicateKeysRule to remove grouping keys that are still required.

This change:

• Corrects equality-derived functional dependencies for INNER, LEFT, and RIGHT joins, respecting the null-generating side of outer joins.
• Preserves valid input functional dependencies through outer joins without incorrectly deriving the reverse dependency from the join equality.
• Maps aggregate input group ordinals to aggregate output ordinals before publishing functional-dependency metadata.
• Avoids equality-derived dependencies for FLOAT, REAL, DOUBLE, and INTERVAL types, including nested occurrences.
• Avoids unsafe expression-derived grouping dependencies for those same types.
• Adds a reusable SqlTypeUtil predicate traversal for scalar and nested types.
• Adds regression coverage for each correctness case.

A basic valid duplicate-key removal remains supported:

SELECT t1.col1, t2.col3, COUNT(*)
FROM t1
JOIN t2 ON t1.col1 = t2.col3
GROUP BY t1.col1, t2.col3;

For this inner join, either equivalent equality key may be removed. The new safeguards prevent that reasoning from being applied where null generation, ordinal mapping, or non-reflexive type semantics make it unsound.

Testing

• ./gradlew :core:test --tests org.apache.calcite.sql.type.SqlTypeUtilTest --tests org.apache.calcite.test.AggregateRemoveDuplicateKeysRuleTest --tests org.apache.calcite.test.RelMetadataTest.testFunctionalDependency*
• ./gradlew :core:checkstyleMain :core:checkstyleTest
• git diff --check upstream/main...HEAD

The focused test run completed 49 tests with 0 failures.

[mihaibudiu]

CI doesn't like your changes

[darpan-14]

CI is happy now. 😄

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
90.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[mihaibudiu]

why are intervals unsafe?

[darpan-14]

They are safe, it was an oversight from my side 😓

I see Calcite normalises intervals under the hood. I will remove this check for intervals.