Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/15718#discussion_r86301490
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeCreator.scala
---
@@ -172,110 +174,80 @@ case class CreateMap(children: Seq[Expression])
extends Expression {
}
/**
- * Returns a Row containing the evaluation of all children expressions.
+ * An expression representing a not yet available attribute name. This
expression is unevaluable
+ * and as its name suggests it is a temporary place holder until we're
able to determine the
+ * actual attribute name.
*/
-@ExpressionDescription(
- usage = "_FUNC_(col1, col2, col3, ...) - Creates a struct with the given
field values.")
-case class CreateStruct(children: Seq[Expression]) extends Expression {
-
- override def foldable: Boolean = children.forall(_.foldable)
-
- override lazy val dataType: StructType = {
- val fields = children.zipWithIndex.map { case (child, idx) =>
- child match {
- case ne: NamedExpression =>
- StructField(ne.name, ne.dataType, ne.nullable, ne.metadata)
- case _ =>
- StructField(s"col${idx + 1}", child.dataType, child.nullable,
Metadata.empty)
- }
- }
- StructType(fields)
- }
-
+case object NamePlaceholder extends LeafExpression with Unevaluable {
--- End diff --
@hvanhovell Although this is merged, I have a question about this
`NamePlaceholder`.
Is it necessary? Actually it has no function and will be replaced with the
field name later in analysis.
The resolution of `CreateNamedStruct` is depended on the field expressions,
actually. So if we directly use the field name, seems it is no harm too?
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