zhidongqu-db opened a new pull request, #55681: URL: https://github.com/apache/spark/pull/55681
### What changes were proposed in this pull request? This is the first of two PRs implementing https://issues.apache.org/jira/browse/SPARK-56395. It introduces the SQL grammar, logical plan, analyzer checks, and optimizer rewrite. The DataFrame / PySpark / Spark Connect API surface is split into a follow-up PR. **SQL syntax** ``` left_relation [ INNER | LEFT [ OUTER ] ] JOIN right_relation nearest_by_clause nearest_by_clause: { APPROX | EXACT } NEAREST [ num_results ] BY { DISTANCE | SIMILARITY } ranking_expression ``` Only INNER (default) and LEFT OUTER join types are supported. num_results is a positive integer in [1, 100000], default 1. DISTANCE ranks smallest first; SIMILARITY ranks largest first. **Example:** ``` CREATE TEMP VIEW users(user_id, score) AS VALUES (1, 10.0), (2, 20.0), (3, 30.0); CREATE TEMP VIEW products(product, pscore) AS VALUES ('A', 11.0), ('B', 22.0), ('C', 5.0); SELECT u.user_id, p.product FROM users u JOIN products p APPROX NEAREST 2 BY DISTANCE abs(u.score - p.pscore); ``` **Parsed Plan** ``` 'Project ['u.user_id, 'p.product] +- 'NearestByJoin Inner, approx=true, k=2, direction=NearestByDistance, rank='abs('u.score - 'p.pscore) :- 'SubqueryAlias u : +- 'UnresolvedRelation [users] +- 'SubqueryAlias p +- 'UnresolvedRelation [products] ``` **Optimized Plan** ``` Project [user_id#1, product#3] +- Generate inline(__nearest_matches__#7), [product#3, pscore#4], outer=false +- Aggregate [__qid#5], [first(user_id#1) AS user_id#1, first(score#2) AS score#2, min_by(struct(product#3, pscore#4), abs(score#2 - pscore#4), 2) AS __nearest_matches__#7] +- Join LeftOuter :- Project [user_id#1, score#2, : monotonically_increasing_id() AS __qid#5] : +- LocalRelation [user_id#1, score#2] +- LocalRelation [product#3, pscore#4] ``` **Physical Plan** ``` *(3) Project [user_id#1, product#3] +- *(3) Generate inline(__nearest_matches__#7), [user_id#1, score#2], false, [product#3, pscore#4] +- ObjectHashAggregate(keys=[__qid#5], functions=[first(user_id#1), first(score#2), min_by(struct(product#3, pscore#4), abs(score#2 - pscore#4), 2)]) +- Exchange hashpartitioning(__qid#5, 200) +- ObjectHashAggregate(keys=[__qid#5], functions=[partial_first(user_id#1), partial_first(score#2), partial_min_by(struct(product#3, pscore#4), abs(score#2 - pscore#4), 2)]) +- BroadcastNestedLoopJoin BuildRight, LeftOuter :- *(1) Project [user_id#1, score#2, : monotonically_increasing_id() AS __qid#5] : +- LocalTableScan [user_id#1, score#2] +- BroadcastExchange IdentityBroadcastMode +- LocalTableScan [product#3, pscore#4] ``` ### Why are the changes needed Design and rationale: see the SPIP linked from https://issues.apache.org/jira/browse/SPARK-56395. ### Does this PR introduce _any_ user-facing change? Yes — new SQL syntax (NEAREST BY clause). Five new non-reserved keywords (APPROX, EXACT, NEAREST, DISTANCE, SIMILARITY) added to the grammar; existing queries are unaffected because they're non-reserved. New error class NEAREST_BY_JOIN. ### How was this patch tested? PlanParserSuite,RewriteNearestByJoinSuite,SQLQueryTestSuite,SparkConnectDatabaseMetaDataSuite,ThriftServerWithSparkContextSuite ### Was this patch authored or co-authored using generative AI tooling? Generated-by: Claude Code (Opus 4.7), human-reviewed and tested Closes #55629 from dilipbiswal/SPARK-56395-CATALYST. Lead-authored-by: Dilip Biswal <[email protected]> <!-- Thanks for sending a pull request! Here are some tips for you: 1. If this is your first time, please read our contributor guidelines: https://spark.apache.org/contributing.html 2. Ensure you have added or run the appropriate tests for your PR: https://spark.apache.org/developer-tools.html 3. 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