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https://issues.apache.org/jira/browse/SOLR-16239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17550488#comment-17550488
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Joel Bernstein commented on SOLR-16239:
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One of the first joins that would be nice to support is an aggregation that
joins to return the grouping key from a different collection. This allows for
query plans that aggregate first and then join to fetch the group key following
the aggregation. Here is an example:
{code:java}
SELECT c.product_name, COUNT(*) AS cnt FROM signals s
LEFT JOIN catalog c ON s.product_id = c.product_id
GROUP BY c.product_name
ORDER BY cnt desc
LIMIT 25
{code}
This could be rewritten to a very efficient:
{code:java}
select(fetch(facet(products, buckets="product_id"),
on="product_id=product_id",
fl="product_name"),
count as cnt,
product_name)
{code}
> Add Join query plans to Solr SQL
> --------------------------------
>
> Key: SOLR-16239
> URL: https://issues.apache.org/jira/browse/SOLR-16239
> Project: Solr
> Issue Type: New Feature
> Security Level: Public(Default Security Level. Issues are Public)
> Components: Parallel SQL
> Reporter: Joel Bernstein
> Priority: Major
> Labels: RobustSQL
>
> This is an umbrella ticket for adding join query plans for Solr SQL.
> Solr 9 adds significant performance improvements to the export handler. These
> improvements were done in part to support fast distributed joins in Solr SQL.
> Streaming Expressions already supports hash joins and merge joins and has
> limited support for nested loop joins (fetch). What needs to be done is to
> add Rules to the Calcite planner that pushes the joins down to the SQL
> handler.
> Calcite also has the ability to execute joins so part of this work will also
> be to gracefully fall back to Calcite's join engine.
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