[
https://issues.apache.org/jira/browse/SPARK-51884?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Wenchen Fan resolved SPARK-51884.
---------------------------------
Fix Version/s: 4.1.0
Resolution: Fixed
Issue resolved by pull request 50838
[https://github.com/apache/spark/pull/50838]
> Subquery Definition Changes For Adding Support For Nested Correlated
> Subqueries
> -------------------------------------------------------------------------------
>
> Key: SPARK-51884
> URL: https://issues.apache.org/jira/browse/SPARK-51884
> Project: Spark
> Issue Type: Sub-task
> Components: Optimizer, SQL
> Affects Versions: 4.1.0
> Reporter: Avery Qi
> Assignee: Avery Qi
> Priority: Major
> Labels: pull-request-available
> Fix For: 4.1.0
>
>
> Newly added argument for SubqueryExpression: OuterScopeAttrs.
> `OuterScopeAttrs` contains attributes cannot be resolved in the containing
> query of the subquery or the subquery itself, but can be resolved in the
> whole query plan.
> h2. The task design includes:
> * Add `OuterScopeAttrs` and related getter and setter methods for
> SubqueryExpression
> * All attributes in `OuterScopeAttrs` must be contained in the `OuterAttrs`
> AttributeSet of SubqueryExpression
> * Update the usage of SubqueryExpression and classes extending
> SubqueryExpression
> * Update SubqueryExpression.references to be `AttributeSet(outerAttrs) –
> AttributeSet(outerScopeAttrs)`
> h2. Why we need the change?
> Spark only supports one layer of correlation now and does not support nested
> correlation.
> For example,
> SELECT col1 FROM VALUES (1, 2) t1 (col1, col2) WHERE EXISTS ( SELECT col1
> FROM VALUES (1, 2) t2 (col1, col2) WHERE t2.col2 == MAX(t1.col2)
> )GROUP BY col1;
>
> is supported and
> SELECT col1 FROM VALUES (1, 2) t1 (col1, col2) WHERE EXISTS ( SELECT col1
> FROM VALUES (1, 2) t2 (col1, col2) WHERE t2.col2 == ( SELECT MAX(t1.col2)
> )
> )GROUP BY col1;
>
> is not supported.
> The reason spark does not support it is because the Analyzer and Optimizer
> resolves and plans Subquery in a recursive way.
> The definition change for the SubqueryExpression adds the metadata
> OuterScopeAttrs which helps later rewrites for the Analyzer and Optimizer.
> h2. High Level Design
> [https://docs.google.com/document/d/1EGB48ArLQ04OZvb-zx_VVTJ8roIoCPwSRw4vTVuDY7o/edit?usp=sharing]
>
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org
For additional commands, e-mail: issues-h...@spark.apache.org
