[GitHub] [calcite] chunweilei commented on a change in pull request #2053: [CALCITE-4102] Some improvements to aggregate related operations

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chunweilei commented on a change in pull request #2053:
URL: https://github.com/apache/calcite/pull/2053#discussion_r454061401



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File path: core/src/main/java/org/apache/calcite/rel/core/Aggregate.java
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@@ -548,19 +538,22 @@ public static boolean isRollup(ImmutableBitSet groupSet,
      *
      * @see #isRollup(ImmutableBitSet, List) */
     public static List<Integer> getRollup(List<ImmutableBitSet> groupSets) {
-      final Set<Integer> set = new LinkedHashSet<>();
+      final List<Integer> rollUpBits = new ArrayList<>(groupSets.size() - 1);
       ImmutableBitSet g = null;
       for (ImmutableBitSet bitSet : groupSets) {
         if (g == null) {
           // First item must equal groupSet
         } else {
           // Each subsequent items must be a subset with one fewer bit than the
           // previous item
-          set.addAll(g.except(bitSet).toList());
+          ImmutableBitSet diff = g.except(bitSet);

Review comment:
       Would there be duplicate values since Set is changed to List?




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