Aleksandr Efimov created CALCITE-7828:
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Summary: Aggregate whose grouping sets include () returns no rows
on empty input
Key: CALCITE-7828
URL: https://issues.apache.org/jira/browse/CALCITE-7828
Project: Calcite
Issue Type: Bug
Components: core
Affects Versions: 1.42.0
Reporter: Aleksandr Efimov
ROLLUP(a) is GROUPING SETS ((a), ()), and the () set yields one row even when
the input is empty, as a query with no GROUP BY does (CALCITE-1059). Calcite
returns no rows instead:
{code:sql}
SELECT a, COUNT(*) AS c FROM (VALUES (1)) AS t(a) WHERE FALSE GROUP BY
ROLLUP(a);
{code}
The expected result is one row, (NULL, 0). CUBE(a, b) and GROUPING SETS ((a),
()) lose the row for () in the same way.
Two places drop the row. {{PruneEmptyRules.AGGREGATE_INSTANCE}} replaces the
aggregate with an empty {{Values}}, because its guard,
{{Aggregate.isNotGrandTotal}}, only checks that the group count is greater than
0. With that rule removed, the plan keeps {{EnumerableAggregate(group=[{0}],
groups=[[{0}, {}]])}} over the empty {{Values}}, but the query still returns no
rows.
Reproduced on 1.42.0 and on main (4e9460600c).
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