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https://issues.apache.org/jira/browse/CALCITE-1753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15969766#comment-15969766
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Julian Hyde commented on CALCITE-1753:
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We could add an annotation (or other metadata) to UDFs specifying how they
treat null values.
The majority of SQL functions return null if any of their arguments are null
(and aggregate functions are not even invoked if argument is null) so I think
that should be the default.
There's an additional property which is whether they ONLY return null if their
inputs are null. {{Nullif}} is a counter-example: for example {{Nullif(5, 5)}}
evaluates to null.
> ProjectJoinTransposeRule with preserveExprCondition pushes projects below
> outer-joins
> -------------------------------------------------------------------------------------
>
> Key: CALCITE-1753
> URL: https://issues.apache.org/jira/browse/CALCITE-1753
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: MinJi Kim
> Assignee: Julian Hyde
>
> I am pushing case statements past joins using ProjectJoinTransposeRule. For
> inner joins, the current behavior seems fine, but outer joins can lead to
> weird behavior, where the project is below the join and nulls can cause
> issues.
> {code}
> select
> count(*), case when t3.a3 is not null then t3.a3 else 100 end
> from
> t1 left outer join t3 on t1.c1 = t3.c3
> group by
> case when t3.a3 is not null then t3.a3 else 100 end
> order by
> case when t3.a3 is not null then t3.a3 else 100 end
> {code}
> Currently, ProjectJoinTransposeRule will push the case statement below the
> join as below. But, this case statement shouldn't be pushed. The query
> shouldn't return null but instead as 100 for any "unmatched" join condition
> since it is a left outer join with a case statement. But, the current plan
> would not prevent that.
>
> {code}
> LogicalProject with case statement
> LogicalJoin
> LogicalTableScan(table=[t1])
> LogicalTableScan(table=[t3])
> {code}
> {code}
> LogicalProject
> LogicalJoin
> LogicalProject with case statement
> LogicalTableScan(table=[t1])
> LogicalTableScan(table=[t3])
> {code}
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