[GitHub] [spark] cloud-fan commented on a change in pull request #32201: [SPARK-35026][SQL] Support nested CUBE/ROLLUP/GROUPING SETS in GROUPING SETS

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cloud-fan commented on a change in pull request #32201:
URL: https://github.com/apache/spark/pull/32201#discussion_r617710259



##########
File path: docs/sql-ref-syntax-qry-select-groupby.md
##########
@@ -113,7 +116,18 @@ aggregate_name ( [ DISTINCT ] expression [ , ... ] ) [ FILTER ( WHERE boolean_ex
         (warehouse, location),
         (warehouse, size),
         (warehouse))`.
- 
+    
+    `GROUP BY warehouse, GROUPING SETS((env), GROUPING SETS((product), ()), GROUPING SETS((location, size), (location), (size), ()))`

Review comment:
       Can we give an explanation on the behavior instead of examples only? We have a good explaination for the mixed case:
   ```
   For multiple `GROUPING SETS` in the `GROUP BY` clause, we generate
   a single `GROUPING SETS` by doing a cross-product of the original `GROUPING SETS`s.
   ```
   
   Can we do the same for nested case?




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