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https://issues.apache.org/jira/browse/OPTIQ-346?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julian Hyde closed OPTIQ-346.
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Close issues resolved in release 0.9.0-incubating (2014-08-25).
> Add commutative join rule
> -------------------------
>
> Key: OPTIQ-346
> URL: https://issues.apache.org/jira/browse/OPTIQ-346
> Project: Optiq
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Fix For: 0.9.0-incubating
>
>
> Add a rule that transforms joins according to the commutativity rule ((a join
> b) join c) -> (a join (b join c)).
> The rule would assume that conditions are pushed down as far as possible, and
> would push down conditions as far as possible. It remains TBD whether the
> rule would permit creation of cartesian joins.
> This rule compliments existing associativity rules for (SwapJoinRule) and
> exchange rules (two variants of PushJoinThroughJoinRule).
> When combined with the other rules, this will be able to find all possible
> join plans, including bushy plans. But it will increase the size of the
> search space, so we will need to be careful not to do exhaustive search for
> queries with more than, say, 7 joins. A heuristic/greedy algorithm will be
> needed for those cases.
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