[GitHub] [calcite] zabetak commented on a change in pull request #2623: CALCITE-4913 Correlated variables in a select list are not deduplicated

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zabetak commented on a change in pull request #2623:
URL: https://github.com/apache/calcite/pull/2623#discussion_r761868245



##########
File path: core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
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@@ -4346,7 +4336,21 @@ private void convertSelectList(
 
     relBuilder.push(bb.root())
         .projectNamed(exprs, fieldNames, true);
-    bb.setRoot(relBuilder.build(), false);
+
+    RelNode project = relBuilder.build();
+
+    final RelNode r;
+    final CorrelationUse p = getCorrelationUse(bb, project);
+    if (p != null) {
+      assert p.r instanceof Project;
+      Project proj = (Project) p.r;
+      r = LogicalProject.create(proj.getInput(), proj.getHints(),

Review comment:
       I've seen that this pattern appears in other places in `SqlToRelConverter` but it is a bit weird that from one hand we are asserting that the project is an instance of a superclass (`Project`) and on the other hand we are creating a `LogicalProject`. Can we use the `relbuilder` to create the new project? Would it be better to rely on `project#copy`?




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