[GitHub] [druid] maytasm commented on a change in pull request #9648: SQL: More straightforward handling of join planning.

[GitBox <gi...@apache.org>]

maytasm commented on a change in pull request #9648:
URL: https://github.com/apache/druid/pull/9648#discussion_r415012376



##########
File path: sql/src/main/java/org/apache/druid/sql/calcite/rel/DruidJoinQueryRel.java
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@@ -395,4 +365,14 @@ private static boolean computeRightRequiresSubquery(final DruidRel<?> right)
 
     return Pair.of(rightPrefix, signatureBuilder.build());
   }
+
+  private static DruidRel<?> getSomeDruidChild(final RelNode child)
+  {
+    if (child instanceof DruidRel) {
+      return (DruidRel<?>) child;
+    } else {
+      final RelSubset subset = (RelSubset) child;

Review comment:
       subset of equivalent rels -> Does this imply that the cost of each RelNode will be equal? I saw that computeLeftRequiresSubquery does returns different depending on which child we pick from the list of RelList. This then result in a very very different cost since a child that results in requiring subquery will have very high cost and a child that doesnt will have a much lower cost. 
   
   More specifically, I saw two RelNode in the list. One RelNode has a filter = null and the other has "filter":{"type":"selector","dimension":"v","value":"xa","extractionFn":null}




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