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Posted to issues@spark.apache.org by "Yuming Wang (JIRA)" <ji...@apache.org> on 2019/07/14 14:04:00 UTC

[jira] [Created] (SPARK-28385) SELECT DISTINCT ON ( expression [, ...] ) syntax

Yuming Wang created SPARK-28385:
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             Summary: 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


{{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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