JoshRosen commented on a change in pull request #24557: [SPARK-27653][SQL] Add max_by() SQL aggregate function URL: https://github.com/apache/spark/pull/24557#discussion_r282141704
########## File path: sql/core/src/test/scala/org/apache/spark/sql/DataFrameAggregateSuite.scala ########## @@ -782,4 +782,47 @@ class DataFrameAggregateSuite extends QueryTest with SharedSQLContext { val countAndDistinct = df.select(count("*"), countDistinct("*")) checkAnswer(countAndDistinct, Row(100000, 100)) } + + test("max_by") { + val yearOfMaxEarnings = + sql("SELECT course, max_by(year, earnings) FROM courseSales GROUP BY course") + checkAnswer(yearOfMaxEarnings, Row("dotNET", 2013) :: Row("Java", 2013) :: Nil) + + checkAnswer( + sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', 20)) AS tab(x, y)"), + Row("b") :: Nil + ) + + checkAnswer( + sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', null)), (('c', 20)) AS tab(x, y)"), + Row("c") :: Nil + ) + + checkAnswer( + sql("SELECT max_by(x, y) FROM VALUES (('a', null)), (('b', null)), (('c', 20)) AS tab(x, y)"), + Row("c") :: Nil + ) + + checkAnswer( + sql("SELECT max_by(x, y) FROM VALUES (('a', 10)), (('b', 50)), (('c', null)) AS tab(x, y)"), + Row("b") :: Nil + ) + + checkAnswer( + sql("SELECT max_by(x, y) FROM VALUES (('a', null)), (('b', null)) AS tab(x, y)"), Review comment: This returns `null` because all values of the ordering column are `null`? That seems to match Presto behavior: ``` SELECT max_by(x, y) FROM ( VALUES ('a', null), ('b', null) ) AS tab (x, y) ``` also returns `null` in Presto :thumbsup: ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: reviews-unsubscr...@spark.apache.org For additional commands, e-mail: reviews-h...@spark.apache.org