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https://issues.apache.org/jira/browse/CALCITE-6402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17844737#comment-17844737
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Julian Hyde edited comment on CALCITE-6402 at 5/8/24 6:41 PM:
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I agree with your analysis.
It seems we need a means other than {{int groupCount}} to determine whether the
output will contain rows that are the aggregate of zero rows. Can you propose
something? I would be open to obsoleting {{groupCount}} (i.e. deprecating the
method and ceasing to use it) and using something else.
When implementing CALCITE-704, I [commented
that|https://github.com/apache/calcite/blob/7ef829e17cf382e34b2c5ee36a664d98a7258c31/core/src/main/java/org/apache/calcite/sql/SqlFilterOperator.java#L103]
that "[pretending that group-count is 0] tells the aggregate function that it
might be invoked with 0 rows in a group". I think we should continue with that
approach, or maybe make it more explicit.
was (Author: julianhyde):
I agree with your analysis.
It seems we need a means other than {{int groupCount}} to determine whether the
output will contain rows that are the aggregate of zero rows. Can you propose
something? I would be open to obsoleting {{groupCount}} (i.e. deprecating the
method and ceasing to use it) and using something else.
> Aggregates implied in grouping sets have a wrong nullability at validation
> stage
> --------------------------------------------------------------------------------
>
> Key: CALCITE-6402
> URL: https://issues.apache.org/jira/browse/CALCITE-6402
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.36.0
> Reporter: Claude Brisson
> Priority: Major
>
> As long as the empty set is present among the grouping sets, which is always
> the case for CUBE and ROLLAP, the (unfiltered) result will contain a row with
> the global aggregate. And on such a row, most standard aggregate functions
> are nullable (even on a non-null column, for the empty rowset).
> But the SUM function, for instance, has the following return type inference:
> {code}
> public static final SqlReturnTypeInference AGG_SUM = opBinding -> {
> final RelDataTypeFactory typeFactory = opBinding.getTypeFactory();
> final RelDataType type = typeFactory.getTypeSystem()
> .deriveSumType(typeFactory, opBinding.getOperandType(0));
> if (opBinding.getGroupCount() == 0 || opBinding.hasFilter()) {
> return typeFactory.createTypeWithNullability(type, true);
> } else {
> return type;
> }
> };
> {code}
> If the operand is not nullable, since the group count will be non-zero for a
> rollup, a cube or a grouping sets containing the empty set.
> It seems to me that the group count itself is not a sufficient information to
> determine the nullability, we may be lacking a boolean stating whether the
> empty group is implied, or the complete list of groups instead of the groups
> count.
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