hannerwang commented on a change in pull request #2458:
URL: https://github.com/apache/calcite/pull/2458#discussion_r675280158
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File path: core/src/main/java/org/apache/calcite/tools/RelBuilder.java
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@@ -934,7 +934,15 @@ public GroupKey groupKey(ImmutableBitSet groupSet) {
*
* <p>This method of creating a group key does not allow you to group on new
* expressions, only column projections, but is efficient, especially when
you
- * are coming from an existing {@link Aggregate}. */
+ * are coming from an existing {@link Aggregate}.
+ *
+ * <p>This method of creating a group key allow you to create groupKey be a
Review comment:
How about "This method of creating a group key allows you to create a
group key which is a superset of the union of the groupingSets, for example:
group by 0, 1, 2, grouping sets((0, 1), 0). When converting RelNode To Sql, the
{@link org.apache.calcite.rel.rel2sql.RelToSqlConverter#visit(Aggregate)} will
generate the superset grouping set, then by having clause filtering it out"
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