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https://issues.apache.org/jira/browse/PHOENIX-167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14159229#comment-14159229
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Maryann Xue commented on PHOENIX-167:
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[~jamestaylor] For IN, the inner query will be a distinct (select distinct
join-keys). For EXISTS, most of the time their inner query is correlated and
they are equivalent to IN sub-queries or complicated correlated sub-queries
(which will be covered by PHOENIX-945). Otherwise, if the inner query has no
reference to the outer query, yes, we should add a LIMIT here. Good reminder,
thanks, James!
[~anoop.hbase] Yes, think I can work on the documentation after I finish the
entire work of PHOENIX-1167. Thanks a lot for reminding me!
> Support semi/anti-joins
> -----------------------
>
> Key: PHOENIX-167
> URL: https://issues.apache.org/jira/browse/PHOENIX-167
> Project: Phoenix
> Issue Type: Sub-task
> Reporter: James Taylor
> Assignee: Maryann Xue
> Labels: enhancement
> Attachments: 167.patch
>
>
> A semi-join between two tables returns rows from the first table where one or
> more matches are found in the second table. The difference between a
> semi-join and a conventional join is that rows in the first table will be
> returned at most once. Even if the second table contains two matches for a
> row in the first table, only one copy of the row will be returned. Semi-joins
> are written using the EXISTS or IN constructs.
> An anti-join is the opposite of a semi-join and is written using the NOT
> EXISTS or NOT IN constructs.
> There's a pretty good write-up [here]
> (http://www.dbspecialists.com/files/presentations/semijoins.html) on
> semi/anti joins.
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