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https://issues.apache.org/jira/browse/CALCITE-4486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17371573#comment-17371573
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Julian Hyde commented on CALCITE-4486:
--------------------------------------
I discovered that CALCITE-3524 deals with adding sub-query methods to
{{RelBuilder}}. The {{unique}} method should be part of that (or could build on
it). In this task, I think you should add {{RexSubQuery.unique}}, and consider
{{RelBuilder.unique()}} to be out of scope.
> UNIQUE predicate
> ----------------
>
> Key: CALCITE-4486
> URL: https://issues.apache.org/jira/browse/CALCITE-4486
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Priority: Major
>
> 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/].
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