cloud-fan commented on a change in pull request #32017:
URL: https://github.com/apache/spark/pull/32017#discussion_r606954761
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
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@@ -924,11 +947,6 @@ case class SubqueryAlias(
child.output.map(_.withQualifier(qualifierList))
}
- override def metadataOutput: Seq[Attribute] = {
- val qualifierList = identifier.qualifier :+ alias
- child.metadataOutput.map(_.withQualifier(qualifierList))
- }
Review comment:
I think we should only expose the metadata column in a single SELECT
group, e.g. `SELECT _file FROM t`, `SELECT t1._file FROM t1 JOIN t2`.
It's super weird if we can propagate the metadata column through SELECT
groups, e.g. `SELECT s._file FROM (SELECT a, b FROM t) s`. The `s` is a
subquery alias and the subquery has a clear output list which is `a, b`. It may
surprise users if they can access `s._file`.
However, I do agree with @rdblue that simple alias should be supported. For
example, `SELECT t1._file FROM t t1 JOIN t t2`. `SELECT s._file FROM (SELECT
...) s` won't work anyway because `Project` can't propagate the metadata
columns.
That said, let's propagate metadata columns in `SubqueryAlias`
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