Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/10353#discussion_r47893041
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/DataFrame.scala ---
@@ -511,9 +509,26 @@ class DataFrame private[sql](
catalyst.expressions.And(cond, eqTo)
}
+ // Project only one of the join columns.
+ val joinedCols = JoinType(joinType) match {
+ case Inner | LeftOuter | LeftSemi =>
+ usingColumns.map(col => withPlan(joined.left).resolve(col))
+ case RightOuter =>
+ usingColumns.map(col => withPlan(joined.right).resolve(col))
+ case FullOuter =>
+ usingColumns.map { col =>
+ val leftCol = withPlan(joined.left).resolve(col)
+ val rightCol = withPlan(joined.right).resolve(col)
+ Alias(Coalesce(Seq(leftCol, rightCol)), col)()
+ }
+ }
+ // The nullability of output of joined could be different than
original column,
+ // so we can only compare them by exprId
+ val joinRefs =
condition.map(_.references.toSeq.map(_.exprId)).getOrElse(Nil)
+ val resultCols = joinedCols ++ joined.output.filterNot(e =>
joinRefs.contains(e.exprId))
--- End diff --
Nit: Here we can use an `AttributeSet` for convenience:
```scala
val joinRefs = AttributeSet(condition.toSeq.flatMap(_.references))
val resultCols = joinedCols ++ joined.output.filterNot(joinRefs.contains)
```
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