AngersZhuuuu commented on a change in pull request #32201:
URL: https://github.com/apache/spark/pull/32201#discussion_r618173234
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File path: docs/sql-ref-syntax-qry-select-groupby.md
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@@ -95,13 +95,17 @@ aggregate_name ( [ DISTINCT ] expression [ , ... ] ) [
FILTER ( WHERE boolean_ex
(product, warehouse, location), (warehouse), (product), (warehouse,
product), ())`.
The N elements of a `CUBE` specification results in 2^N `GROUPING SETS`.
-* **Mixed Grouping Analytics**
+* **Mixed/Nested Grouping Analytics**
- A GROUP BY clause can include multiple `group_expression`s and multiple
`CUBE|ROLLUP|GROUPING SETS`s.
+ A GROUP BY clause can include multiple `group_expression`s and multiple
`CUBE|ROLLUP|GROUPING SETS`s.
+ `GROUPING SETS` can also have nested `CUBE|ROLLUP|GROUPING SETS` clauses,
e.g.
+ `GROUPING SETS(ROLLUP(warehouse, location), CUBE(warehouse, location))`,
+ `GROUPING SETS(warehouse, GROUPING SETS(location, GROUPING
SETS(ROLLUP(warehouse, location), CUBE(warehouse, location))))`.
`CUBE|ROLLUP` is just a syntax sugar for `GROUPING SETS`, please refer to
the sections above for
how to translate `CUBE|ROLLUP` to `GROUPING SETS`. `group_expression` can
be treated as a single-group
`GROUPING SETS` under this context. 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. For example,
+ a single `GROUPING SETS` by doing a cross-product of the original
`GROUPING SETS`s. For nested `GROUPING SETS` in the `GROUPING SETS` clause,
+ we generate a top-level `GROUING SETS` by expand selected grouping sets of
nested group elements. For example,
Review comment:
> It seems your previous example was wrong.
>
> `GROUPING SETS(GROUPING SETS(a, b), GROUPING SETS(c, d))` should be
`GROUPING SETS(a, b, c, d)`, instead of `GROUPING SETS((a, b), (c, d))`
Yea， previous example I miss `()`, current is correct.
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