cloud-fan commented on a change in pull request #23303: [SPARK-26352][SQL]
ReorderJoin should not change the order of columns
URL: https://github.com/apache/spark/pull/23303#discussion_r241258137
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
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@@ -99,6 +99,14 @@ object ReorderJoin extends Rule[LogicalPlan] with
PredicateHelper {
} else {
createOrderedJoin(input, conditions)
}
+
+ if (p.sameOutput(reordered)) {
+ reordered
+ } else {
+ // Reordering the joins have changed the order of the columns.
+ // Inject a projection to make sure we restore to the expected
ordering.
+ Project(p.output, reordered)
Review comment:
just for curiosity, we only need this for top-level join? I feel it's ok to
change the columnar order for intermedia joins.
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