rdblue commented on a change in pull request #35395:
URL: https://github.com/apache/spark/pull/35395#discussion_r810701107
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
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@@ -388,3 +391,62 @@ object ExtractSingleColumnNullAwareAntiJoin extends
JoinSelectionHelper with Pre
case _ => None
}
}
+
+/**
+ * An extractor for operations such as DELETE and MERGE that require rewriting
data.
+ *
+ * This class extracts the following entities:
+ * - the row-level command (such as [[DeleteFromTable]]);
+ * - the read relation in the rewrite plan that can be either
[[DataSourceV2Relation]] or
+ * [[DataSourceV2ScanRelation]] depending on whether the planning has already
happened;
+ * - the current rewrite plan.
Review comment:
It would be good to mention why this always finds the read relation
rather than constructing the `RowLevelCommand` with a hard reference to it. My
understanding is that it may be changed by the optimizer. It could be removed
based on the condition and there may be more than one depending on the planning
for UPDATE queries. Is that right?
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