cloud-fan commented on a change in pull request #31666:
URL: https://github.com/apache/spark/pull/31666#discussion_r608690135
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/package.scala
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@@ -201,4 +201,29 @@ package object util extends Logging {
def truncatedString[T](seq: Seq[T], sep: String, maxFields: Int): String = {
truncatedString(seq, "", sep, "", maxFields)
}
+
+ val METADATA_COL_ATTR_KEY = "__metadata_col"
+
+ /**
+ * Hidden columns are a type of metadata column that are not propagated
through subquery aliases,
+ * and are candidates during qualified star expansions.
Review comment:
Can we update the comments? It seems "not propagated through subquery
aliases" is not a difference anymore. The new difference is "hidden column can
be propagated through project".
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