[GitHub] [calcite] libenchao commented on a diff in pull request #3052: [CALCITE-5506] RelToSqlConverter should retain the aggregation logic

["libenchao (via GitHub)" <gi...@apache.org>]

libenchao commented on code in PR #3052:
URL: https://github.com/apache/calcite/pull/3052#discussion_r1183442969


##########
core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java:
##########
@@ -1831,6 +1831,21 @@ && hasSortByOrdinal()) {
         return true;
       }
 
+      if (rel instanceof Project) {
+        Project project = (Project) rel;
+        RelNode input = project.getInput();
+        // Cannot merge because "select 1 from t"
+        // is different from "select 1 from (select count(1) from t)"
+        final boolean hasInputRef = project.getProjects()
+            .stream()
+            .anyMatch(rex -> RexUtil.containsInputRef(rex));
+        final boolean hasAggregate =
+            input instanceof Aggregate && input.getRowType().getFieldCount() > 0;

Review Comment:
   Do you need to add `input.getRowType().getFieldCount() > 0`? (I even doubt that we will produce `RelNode` which has `0` fields)



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