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https://issues.apache.org/jira/browse/CALCITE-5856?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Steven Talbot updated CALCITE-5856:
-----------------------------------
Description:
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 emulating the
"()" grouping set _will_ infer nullable using this strategy, and the type of
your rewritten RelNode will no longer match.
was:
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.
> 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
> Priority: Major
>
> 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 emulating
> the "()" grouping set _will_ infer nullable using this strategy, and the type
> of your rewritten RelNode will no longer match.
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