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https://issues.apache.org/jira/browse/CALCITE-968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15018869#comment-15018869
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Julian Hyde commented on CALCITE-968:
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The stream does not need to be left-most. Stream-join-table and
table-join-stream are both valid.
Not sure of the details, but validateModality is just a means to an end. If I
were you I would write tests for valid and invalid queries and make sure that
the invalid ones produce the most useful possible error messages. If you need
to throw away validateModality and start again, that's fine.
> Support stream joins
> --------------------
>
> Key: CALCITE-968
> URL: https://issues.apache.org/jira/browse/CALCITE-968
> Project: Calcite
> Issue Type: New Feature
> Components: core, stream
> Reporter: Milinda Lakmal Pathirage
> Assignee: Julian Hyde
> Attachments: CALCITE-968-0.patch
>
>
> Stream joins are used to relate information from different streams or stream
> and relation combinations. Calcite lacks (proper) support for
> stream-to-relation joins and stream-to-stream joins.
> stream-to-relation join like below fails at the SQL validation stage.
> select stream orders.orderId, orders.productId, products.name from orders
> join products on orders.productId = products.id
> But if 'products' is a stream, the query is valid according to Calcite, even
> though the stream-to-stream join in above query is not valid due to unbounded
> nature of streams.
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