Perrine Letellier created SPARK-20969:
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Summary: last() aggregate function fails returning the right
answer with ordered windows
Key: SPARK-20969
URL: https://issues.apache.org/jira/browse/SPARK-20969
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.1.1
Reporter: Perrine Letellier
{code}
scala> val df = sc.parallelize(List(("i1", 1, "desc1"), ("i1", 1, "desc2"),
("i1", 2, "desc3"))).toDF("id", "ts", "desc")
scala> val window = Window.partitionBy("id").orderBy(col("ts").asc)
scala> df.withColumn("last", last(col("description")).over(window)).show
+---+---+-----+-----+
| id| ts| description| last|
+---+---+-----+-----+
| i1| 1|desc1|desc2|
| i1| 1|desc2|desc2|
| i1| 2|desc3|desc3|
+---+---+-----+-----+
{code}
However what is expected is the same answer as if asking for `first()` with a
window with descending order.
{code}
scala> val window = Window.partitionBy("id").orderBy(col("ts").desc)
scala> df.withColumn("last", first(col("description")).over(window)).show
+---+---+-----+-----+
| id| ts| description| last|
+---+---+-----+-----+
| i1| 2|desc3|desc3|
| i1| 1|desc1|desc3|
| i1| 1|desc2|desc3|
+---+---+-----+-----+
{code}
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