Steven Talbot created CALCITE-5856:
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Summary: ARG0_NULLABLE_IF_EMPTY should consider GROUPING SETS (..,
())
Key: CALCITE-5856
URL: https://issues.apache.org/jira/browse/CALCITE-5856
Project: Calcite
Issue Type: Bug
Reporter: Steven Talbot
Currently, the rule switches off getGroupCount to determine if an aggregation
is empty. However, "select sum(1) as s from empty group by grouping sets((a),
())" will return null, but getGroupCount() will return non-zero, so the return
type for an operator using ARG0_NULLABLE_IF_EMPTY will incorrectly be marked as
non-nullable (if the input was non-nullable).
As a practical matter, this mostly matters if you try to rewrite GROUPING SETS
to some kind of UNION, at which point the branch of the UNION on the "()"
grouping set _will_ infer nullable using this strategy, and the type of your
rewritten RelNode will no longer match.
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