maropu opened a new pull request #27305: [WIP][SPARK-29701][SQL] Correct behaviours of group analytical queries when empty input given URL: https://github.com/apache/spark/pull/27305 <!-- 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. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP][SPARK-XXXX] Your PR title ...'. 4. Be sure to keep the PR description updated to reflect all changes. 5. Please write your PR title to summarize what this PR proposes. 6. If possible, provide a concise example to reproduce the issue for a faster review. --> ### What changes were proposed in this pull request? <!-- Please clarify what changes you are proposing. The purpose of this section is to outline the changes and how this PR fixes the issue. If possible, please consider writing useful notes for better and faster reviews in your PR. See the examples below. 1. If you refactor some codes with changing classes, showing the class hierarchy will help reviewers. 2. If you fix some SQL features, you can provide some references of other DBMSes. 3. If there is design documentation, please add the link. 4. If there is a discussion in the mailing list, please add the link. --> (This is another approach of #27233) This PR intends to fix a bug when empty input given in group analytical queries (e.g., GROUPING SETS). For example, a query below with empty input has a different answer between Spark and PostgreSQL: ``` postgres=# create table gstest_empty (a integer, b integer, v integer); CREATE TABLE postgres=# select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),()); a | b | sum | count ---+---+-----+------- | | | 0 (1 row) scala> sql("""select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),())""").show +---+---+------+--------+ | a| b|sum(v)|count(1)| +---+---+------+--------+ +---+---+------+--------+ ``` In the case, we should follow the PostgreSQL answer. To fix this, this PR modified the existing resolution rules (`ResolveGroupingAnalytics` and `ResolveAggregateFunctions`) to rewrite it as an union query of aggregates with/without keys as follows; ``` scala> sql("""select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),())""").explain(true) == Analyzed Logical Plan == a: int, b: int, sum(v): bigint, count(1): bigint Union :- Aggregate [a#10, b#11, spark_grouping_id#7], [a#10, b#11, sum(cast(v#3 as bigint)) AS sum(v)#5L, count(1) AS count(1)#6L] : +- Expand [List(v#3, a#1, b#2, 0)], [v#3, a#10, b#11, spark_grouping_id#7] : +- Project [v#3, a#1, b#2] : +- Relation[a#1,b#2,v#3] parquet +- Aggregate [null AS a#10, null AS b#11, sum(cast(v#3 as bigint)) AS sum(v)#5L, count(1) AS count(1)#6L] +- Project [v#3] +- Relation[a#1,b#2,v#3] parquet ``` NOTE: This pr also updates the existing test in `OptimizeMetadataOnlyQuerySuite`; it has [the rollup query](https://github.com/apache/spark/pull/27233/files#diff-7d340edd739a1f59d51d5228113fd9edL120) and this PR transforms it into a `union(aggregate with keys, aggregate without keys)` form. The test checks that no metadata-only query happens there, but the `aggregate without keys` side can be optimized by the `OptimizeMetadataOnlyQuery` rule then `testNotMetadataOnly()` fails. To avoid this case, this PR replaces the rollup query with a grouping set one. ### Why are the changes needed? <!-- Please clarify why the changes are needed. For instance, 1. If you propose a new API, clarify the use case for a new API. 2. If you fix a bug, you can clarify why it is a bug. --> For the correct SQL semantics. ### Does this PR introduce any user-facing change? <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If no, write 'No'. --> No. ### How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to add some test cases that check the changes thoroughly including negative and positive cases if possible. If it was tested in a way different from regular unit tests, please clarify how you tested step by step, ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future. If tests were not added, please describe why they were not added and/or why it was difficult to add. --> UTs added.
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