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https://issues.apache.org/jira/browse/SOLR-7584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14972324#comment-14972324
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Dennis Gove commented on SOLR-7584:
-----------------------------------
Could you describe your use-case for joining on facets? I can imagine that a
HashJoin (SOLR-8188) would be good for something like that because it removes
the sort requirement.
Yes, you can apply functions like sum and average on the joined data by
wrapping the resulting joined stream in a RollupStream and using metrics.
> Add Joins to the Streaming API and Streaming Expressions
> --------------------------------------------------------
>
> Key: SOLR-7584
> URL: https://issues.apache.org/jira/browse/SOLR-7584
> Project: Solr
> Issue Type: Improvement
> Components: SolrJ
> Reporter: Dennis Gove
> Priority: Minor
> Labels: Streaming
> Attachments: SOLR-7584.patch, SOLR-7584.patch, SOLR-7584.patch,
> SOLR-7584.patch, SOLR-7584.patch
>
>
> Add InnerJoinStream, LeftOuterJoinStream, and supporting classes to the
> Streaming API to allow for joining between sub-streams.
> At its basic, it would look something like this
> {code}
> innerJoin(
> search(collection1, q=*:*, fl="fieldA, fieldB, fieldC", ...),
> search(collection2, q=*:*, fl="fieldA, fieldD, fieldE", ...),
> on="fieldA=fieldA"
> )
> {code}
> or with multi-field on clauses
> {code}
> innerJoin(
> search(collection1, q=*:*, fl="fieldA, fieldB, fieldC", ...),
> search(collection2, q=*:*, fl="fieldA, fieldD, fieldE", ...),
> on="fieldA=fieldA, fieldB=fieldD"
> )
> {code}
> I'd also like to support the option of doing a hash join instead of the
> default merge join but I haven't yet figured out the best way to express
> that. I'd like to let the user tell us which sub-stream should be hashed (the
> least-cost one).
> Also, I've been thinking about field aliasing and might want to add a
> SelectStream which serves the purpose of allowing us to limit the fields
> coming out and rename fields.
> Depends on SOLR-7554
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