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https://issues.apache.org/jira/browse/HIVE-2337?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Charles Chen reassigned HIVE-2337:
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Assignee: Charles Chen
> Predicate pushdown erroneously conservative with outer joins
> ------------------------------------------------------------
>
> Key: HIVE-2337
> URL: https://issues.apache.org/jira/browse/HIVE-2337
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: Charles Chen
> Assignee: Charles Chen
>
> The predicate pushdown filter is not applying left associativity of joins
> correctly in determining possible aliases for pushing predicates.
> In hive.ql.ppd.OpProcFactory.JoinPPD.getQualifiedAliases, the criteria for
> pushing aliases is specified as:
> {noformat}
> /**
> * Figures out the aliases for whom it is safe to push predicates based on
> * ANSI SQL semantics For inner join, all predicates for all aliases can
> be
> * pushed For full outer join, none of the predicates can be pushed as
> that
> * would limit the number of rows for join For left outer join, all the
> * predicates on the left side aliases can be pushed up For right outer
> * join, all the predicates on the right side aliases can be pushed up
> Joins
> * chain containing both left and right outer joins are treated as full
> * outer join. [...]
> *
> * @param op
> * Join Operator
> * @param rr
> * Row resolver
> * @return set of qualified aliases
> */
> {noformat}
> Since hive joins are left associative, something like "a RIGHT OUTER JOIN b
> LEFT OUTER JOIN c INNER JOIN d" should be interpreted as "((a RIGHT OUTER
> JOIN b) LEFT OUTER JOIN c) INNER JOIN d", so there would be cases where joins
> with both left and right outer joins can have aliases that can be pushed.
> Here, aliases a and d are eligible to be pushed up while the current criteria
> provide that none are eligible.
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