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https://issues.apache.org/jira/browse/SPARK-28385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17004676#comment-17004676
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Takeshi Yamamuro commented on SPARK-28385:
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Based on the document, this is an extension for PostgreSQL. So, I'll close for
now. If necessary, please reopen this.
> SELECT DISTINCT ON ( expression [, ...] ) syntax
> ------------------------------------------------
>
> Key: SPARK-28385
> URL: https://issues.apache.org/jira/browse/SPARK-28385
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Yuming Wang
> Priority: Major
>
> {{SELECT DISTINCT ON ( _{{expression}}_ [, ...] )}} keeps only the first row
> of each set of rows where the given expressions evaluate to equal. The
> {{DISTINCT ON}} expressions are interpreted using the same rules as for
> {{ORDER BY}} (see above). Note that the “first row” of each set is
> unpredictable unless {{ORDER BY}} is used to ensure that the desired row
> appears first. For example:
> {code:sql}
> SELECT DISTINCT ON (location) location, time, report
> FROM weather_reports
> ORDER BY location, time DESC;
> {code}
> https://www.postgresql.org/docs/11/sql-select.html
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