Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13967#discussion_r69139709
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -44,6 +44,58 @@ case class Size(child: Expression) extends
UnaryExpression with ExpectsInputType
}
/**
+ * Returns an unordered array containing the keys of the map.
+ */
+@ExpressionDescription(
+ usage = "_FUNC_(map) - Returns an unordered array containing the keys of
the map.",
+ extended = " > SELECT _FUNC_(map(1, 'a', 2, 'b'));\n [1,2]")
+case class MapKeys(child: Expression)
+ extends UnaryExpression with ExpectsInputTypes {
+
+ override def inputTypes: Seq[AbstractDataType] = Seq(MapType)
+
+ override def dataType: DataType =
ArrayType(child.dataType.asInstanceOf[MapType].keyType)
+
+ override def foldable: Boolean = child.foldable
--- End diff --
this is the default of `UnaryExpression`
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