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https://issues.apache.org/jira/browse/OPTIQ-329?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julian Hyde resolved OPTIQ-329.
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Resolution: Duplicate
> Three-quarter-join: Add flag to JoinRelBase that indicates it should
> eliminate duplicates on right
> --------------------------------------------------------------------------------------------------
>
> Key: OPTIQ-329
> URL: https://issues.apache.org/jira/browse/OPTIQ-329
> Project: Optiq
> Issue Type: New Feature
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> Add a flag to JoinRelBase that indicates it should eliminate duplicates on
> the right-hand side.
> This is functionality similar to semi-join operator in relational algebra,
> and also similar to SemiJoinRel. But:
> 1. This relational expression has the same row type as the corresponding join
> whose flag is false. (If it were executed, it would return dummy values (e.g.
> null or 0) from the fields corresponding to the right-hand input. But in
> practice its consumer would never ask for these fields.) Having the same row
> type helps when mixing it in with other join rules.
> 2. Sub-types of join (e.g. HiveBroadcastJoinRel) would inherit this flag.
> They might disallow particular values of the flag.
> It would be allowed with joinType = {INNER, LEFT}.
> To be decided: If the right input is known not to have duplicates, should the
> flag be set to true, false, or some other value?
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