[teiid-issues] [JBoss JIRA] Resolved: (TEIID-1376) Add support for pushing joins through a union

[Steven Hawkins (JIRA)]

     [ https://issues.jboss.org/browse/TEIID-1376?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins resolved TEIID-1376.
-----------------------------------

    Resolution: Done


Added RuleDecomposeJoin to handle this situation.  The decision to decompose is based upon detecting that each side of the join is a partitioned union (note that non-ansi joins of more than 2 tables may cause the optimization to not detect the appropriate join).  Union partitioning is inferred from the transformation/inline view.  If one (or more) of the union columns is defined by constants and/or has IN predicates in the WHERE clause that make each branch mutually exclusive, then the union is considered partitioned.  e.g. "select 1 as x, y from foo union all select z, a from foo1 where z in (2, 3)" would be considered partitioned on x.  Note that more advanced or explicit partition could be considered in the future.  

The rule currently only looks for situations where at most 1 partition matches from each side.  This is a simplifying assumption based upon the lack of arbitrary sub-plan cloning and potentially making the decision costing dependent.

The release notes have been updated, but the docs still need to add the concept of a partitioned union.  The concept of partitioning will also be used so that views with unions can be inherently insertable.

> Add support for pushing joins through a union
> ---------------------------------------------
>
>                 Key: TEIID-1376
>                 URL: https://issues.jboss.org/browse/TEIID-1376
>             Project: Teiid
>          Issue Type: Feature Request
>          Components: Query Engine
>    Affects Versions: 7.2
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>             Fix For: 7.3
>
>
> Given a query structure such as:
> inner join
>    union all
>      a
>      b
>    union all
>      c
>      d
> where a,b,c,d are access nodes to a source that supports joins and there is a constant column projected by each union branch and that column is used in the join predicates, then we should be able examine
> union all
>   inner join
>     a
>     b
>   inner join
>     a
>     c
> ...
> to determine if any of the joins will no longer be necessary. 
> This is a possible pattern in a multi-source or partitioning scenario.  
> In some scenarios there may not be an actual projected literal, which could be accommodated if a foreign key could be marked as partitioned.

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