[CALCITE-7439] Qualify GROUP BY keys for DISTINCT over joins

[bvolpato]

Summary

RelToSqlConverter emitted an ambiguous GROUP BY key after semi-join rewrites for a DISTINCT query over LEFT JOIN ... USING.

Reproduction query

WITH product_keys AS (
  SELECT p."product_id",
         (SELECT MAX(p3."product_id")
          FROM "foodmart"."product" p3
          WHERE p3."product_id" = p."product_id") AS "mx"
  FROM "foodmart"."product" p
)
SELECT DISTINCT pk."product_id"
FROM product_keys pk
LEFT JOIN "foodmart"."product" p2 USING ("product_id")
WHERE pk."product_id" IN (
  SELECT p4."product_id"
  FROM "foodmart"."product" p4
)

Error before this PR

org.apache.calcite.runtime.CalciteContextException:
From line 12, column 10 to line 12, column 21: Column 'product_id' is ambiguous

Fix

When building GROUP BY keys (and corresponding SELECT keys), qualify one-part identifiers against the SQL join side alias when the aggregate source is a join-shaped input.

Test

• Added RelToSqlConverterTest.testPostgresqlRoundTripDistinctLeftJoinInSubqueryWithSemiJoinRules
• Assert that generated SQL contains GROUP BY "t2"."product_id"
• Ran: ./gradlew :core:test --tests org.apache.calcite.rel.rel2sql.RelToSqlConverterTest
• Result: 563 passed, 0 failed

Disclaimer

The changes were done with the assistance of Codex (gpt-5.3-codex) in response to an actual bug when using Calcite in production. The changes were manually verified prior to sending this to review.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
78.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud