cloud-fan commented on a change in pull request #34575:
URL: https://github.com/apache/spark/pull/34575#discussion_r752936812
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala
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@@ -438,3 +438,22 @@ object VirtualColumn {
val groupingIdName: String = "spark_grouping_id"
val groupingIdAttribute: UnresolvedAttribute =
UnresolvedAttribute(groupingIdName)
}
+
+/**
+ * The internal representation of the hidden metadata column:
+ * set `__metadata_col` to `true` in AttributeReference metadata
+ * - apply() will create a metadata attribute reference
+ * - unapply() will check if an attribute reference is the metadata attribute
reference
+ */
+object MetadataAttribute {
+ def apply(name: String, dataType: DataType): AttributeReference =
+ AttributeReference(name, dataType, true,
Review comment:
shall we allow non-nullable metadata attr? We should probably add one
more parameter in `apply`: `nullable: boolean`
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