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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