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:
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