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https://issues.apache.org/jira/browse/CALCITE-4486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17418403#comment-17418403
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Julian Hyde commented on CALCITE-4486:
--------------------------------------
[~nobigo], Please review the changes I made in
[julianhyde/4486-unique|https://github.com/julianhyde/calcite/tree/4486-unique].
If they're OK I'll squash and merge.
> UNIQUE predicate
> ----------------
>
> Key: CALCITE-4486
> URL: https://issues.apache.org/jira/browse/CALCITE-4486
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Julian Hyde
> Assignee: duan xiong
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.28.0
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> Implement the UNIQUE predicate, as specified by the SQL standard.
> Example:
> {code:java}
> UNIQUE (SELECT publishedIn FROM Book
> WHERE authorId = 3)
> NOT UNIQUE (SELECT publishedIn FROM BOOK
> WHERE authorId = 3)
> {code}
> {{UNIQUE}} returns {{FALSE}} if the query returns two or more rows that do
> not include NULL values and are equal. Like {{EXISTS}}, it never returns
> {{UNKNOWN}}.
> More details at
> [JOOQ|https://www.jooq.org/doc/3.0/manual/sql-building/conditional-expressions/unique-predicate/].
> This Issue support the UNIQUE predicate by set {{isExpand}} to return false,
> so sub-queries are converted to {{RexSubQuery}} expressions and handled later
> by {{SubQueryRemoveRule}}.
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