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https://issues.apache.org/jira/browse/CALCITE-7196?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18022310#comment-18022310
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Mihai Budiu commented on CALCITE-7196:
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We have an example of a query which cannot be decorrelated because of the
Unnest (I commented about this in
https://issues.apache.org/jira/browse/CALCITE-7031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18022304#comment-18022304),
but it can be decorrelated after this rewrite:
{code:sql}
create table t1(arr STRING ARRAY);
create table t2 (id string);
WITH ids AS (
SELECT array_element.id
FROM t1, UNNEST(t1.arr) AS array_element(id)
)
SELECT * FROM ids
WHERE EXISTS (SELECT 1 FROM t2 WHERE t2.id = ids.id)
{code}
> Create an optimization pass which can convert some cases of Correlate +
> Unnest to Unnest
> ----------------------------------------------------------------------------------------
>
> Key: CALCITE-7196
> URL: https://issues.apache.org/jira/browse/CALCITE-7196
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Affects Versions: 1.40.0
> Reporter: Mihai Budiu
> Assignee: Mihai Budiu
> Priority: Minor
>
> Today UNNEST is always compiled into a Correlate + Unnest.
> Some query plans of this shape can be simplified however:
> {code}
> Project
> Correlate
> LeftInput
> Uncollect
> Project(correlatedVariable) // only one field here
> Values
> {code}
> If the Project only preserves fields from the right-side of the Correlate,
> such plans can be rewritten as
> {code}
> Project
> Uncollect
> LeftInput
> {code}
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