[teiid-issues] [JBoss JIRA] (TEIID-2845) MongoDB: Join processing produces wrong results in some cases

[Ramesh Reddy (JIRA)]

     [ https://issues.jboss.org/browse/TEIID-2845?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ramesh Reddy resolved TEIID-2845.
---------------------------------

        Labels: alpha3 mongodb  (was: mongodb)
    Resolution: Done


The $unwind operator behavior was wrongly assumed, where the empty child documents did not produce any documents, so all joins were behaving as INNER joins. See related discussion on it https://groups.google.com/forum/#!topic/mongodb-user/UKYPddRN37E

Used the workaround mentioned on this thread, so that Teiid can generate
* INNER JOIN
* LEFT [OUTER] JOIN (left is assumed to be the parent document)
* CROSS JOIN will be handled by the Teiid engine, as the JOIN capabilities define they only work on KEY based. 
* RIGHT OUTER JOIN either re-written based on which side is parent, otherwise this JOIN produces an exception. One possibility is to extend the "allow-join" semantics to define such that "RIGHT JOIN" is not supported, in which case it can be handled in Teiid query engine.
                
> MongoDB: Join processing produces wrong results in some cases
> -------------------------------------------------------------
>
>                 Key: TEIID-2845
>                 URL: https://issues.jboss.org/browse/TEIID-2845
>             Project: Teiid
>          Issue Type: Bug
>          Components: Misc. Connectors
>    Affects Versions: 8.4
>            Reporter: Ramesh Reddy
>            Assignee: Ramesh Reddy
>              Labels: mongodb, alpha3
>             Fix For: 8.7
>
>
> When two or more tables are used to build single document in the MongoDB, depending upon the JOIN query used it may produce wrong results.
> - support for inner is not turned ON, this should be allowed
> - For example cross-join between parent and embedded table
> - right-join between parent and embedded table
> - depending upon the parent the ordering of left and right join 

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