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https://issues.apache.org/jira/browse/TAJO-1517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14395449#comment-14395449
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Hyunsik Choi commented on TAJO-1517:
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I think that INTERSECT can be easily implemented with SEMI JOIN + SELECT
DISTINCT. Of course, we can design new physical operator for more efficient
processing later.
BTW, {{INTERSECT ALL}} may be hard to use semi join due to the reason you
mentioned. So, I recommend implementing new physical operator for it. Probably,
some sort-based approach that compares two sorted rows of both tables would be
work well.
> Implement INTERSECT
> -------------------
>
> Key: TAJO-1517
> URL: https://issues.apache.org/jira/browse/TAJO-1517
> Project: Tajo
> Issue Type: Sub-task
> Reporter: Keuntae Park
>
> {code}
> query1 INTERSECT [ALL] query2
> {code}
> INTERSECT returns all rows that are both in the result of query1 and in the
> result of query2.
> Duplicate rows are eliminated unless INTERSECT ALL is used.
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