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Posted to issues@spark.apache.org by "Apache Spark (Jira)" <ji...@apache.org> on 2022/10/21 22:29:00 UTC
[jira] [Commented] (SPARK-40862) Unexpected operators when rewriting scalar subqueries with non-deterministic expressions
[ https://issues.apache.org/jira/browse/SPARK-40862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17622508#comment-17622508 ]
Apache Spark commented on SPARK-40862:
--------------------------------------
User 'allisonwang-db' has created a pull request for this issue:
https://github.com/apache/spark/pull/38336
> Unexpected operators when rewriting scalar subqueries with non-deterministic expressions
> ----------------------------------------------------------------------------------------
>
> Key: SPARK-40862
> URL: https://issues.apache.org/jira/browse/SPARK-40862
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.4.0
> Reporter: Allison Wang
> Priority: Major
>
> Since SPARK-28379, Spark has supported non-aggregated single-row correlated subqueries. SPARK-40800 handles the majority of the cases where projects can be collapsed. But Spark can throw exceptions for single-row subqueries with non-deterministic expressions. For example:
> {code:java}
> CREATE TEMP VIEW t1 AS SELECT ARRAY('a', 'b') a
> SELECT (
> SELECT array_sort(a, (i, j) -> rank[i] - rank[j])[0] + r + r AS sorted
> FROM (SELECT MAP('a', 1, 'b', 2) rank, rand() as r)
> ) FROM t1{code}
> This throws an exception:
> {code:java}
> Unexpected operator Join Inner
> :- Aggregate [[a,b]], [[a,b] AS a#253]
> : +- OneRowRelation
> +- Project [map(keys: [a,b], values: [1,2]) AS rank#241, rand(86882494013664043) AS r#242]
> +- OneRowRelation
> in correlated subquery{code}
> This is because when Spark rewrites correlated subqueries, it checks whether a scalar subquery is subject to the COUNT bug. It splits the query into parts above the aggregate, the aggregate, and the parts below the aggregate (see `splitSubquery` in the `RewriteCorrelatedScalarSubquery` rule).
> This pattern is very restrictive and does not work well with non-aggregated single-row subqueries. We should fix this issue.
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