EnricoMi commented on code in PR #37407:
URL: https://github.com/apache/spark/pull/37407#discussion_r958680962
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sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala:
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@@ -2094,6 +2095,23 @@ class Dataset[T] private[sql](
* This is equivalent to calling `Dataset#unpivot(Array, Array, String,
String)`
* where `values` is set to all non-id columns that exist in the DataFrame.
*
+ * Note: A column that is referenced by an id column expression is
considered an id column itself.
+ * For instance `$"id" * 2` references column `id`, so `id` is considered an
id column and not a
+ * value column:
+ * {{{
+ * val df = Seq((1, 11, 12L), (2, 21, 22L)).toDF("id", "int", "long")
+ * df.unpivot(Array($"id" * 2), "var", "val").show()
+ * // output:
+ * // +--------+--------+-----+
+ * // |(id * 2)|variable|value|
+ * // +--------+--------+-----+
+ * // | 2| int| 11|
+ * // | 2| long| 12|
+ * // | 4| int| 21|
+ * // | 4| long| 22|
+ * // +--------+--------+-----+
Review Comment:
fixed
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