Github user skambha commented on a diff in the pull request:
https://github.com/apache/spark/pull/17185#discussion_r207635526
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala
---
@@ -262,17 +262,47 @@ abstract class Star extends LeafExpression with
NamedExpression {
*/
case class UnresolvedStar(target: Option[Seq[String]]) extends Star with
Unevaluable {
- override def expand(input: LogicalPlan, resolver: Resolver):
Seq[NamedExpression] = {
+ /**
+ * Returns true if the nameParts match the qualifier of the attribute
+ *
+ * There are two checks: i) Check if the nameParts match the qualifier
fully.
+ * E.g. SELECT db.t1.* FROM db1.t1 In this case, the nameParts is
Seq("db1", "t1") and
+ * qualifier of the attribute is Seq("db1","t1")
+ * ii) If (i) is not true, then check if nameParts is only a single
element and it
+ * matches the table portion of the qualifier
+ *
+ * E.g. SELECT t1.* FROM db1.t1 In this case nameParts is Seq("t1") and
+ * qualifier is Seq("db1","t1")
+ * SELECT a.* FROM db1.t1 AS a
+ * In this case nameParts is Seq("a") and qualifier for
+ * attribute is Seq("a")
+ */
+ private def matchedQualifier(
+ attribute: Attribute,
--- End diff --
The database information gets carried over based on the lookupRelation
logic. Details are in Section 3.3.3 in the design doc
[here](https://drive.google.com/file/d/1zKm3aNZ3DpsqIuoMvRsf0kkDkXsAasxH/view)
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