[
https://issues.apache.org/jira/browse/CALCITE-7789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18116287#comment-18116287
]
Stamatis Zampetakis commented on CALCITE-7789:
----------------------------------------------
I am happy to explore any other solution suggested by the community so let me
know if you have other ideas.
> Conditionally skip simplifications for certain expressions
> ----------------------------------------------------------
>
> Key: CALCITE-7789
> URL: https://issues.apache.org/jira/browse/CALCITE-7789
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
>
> In the past there were various discussions about incorrect simplifications in
> the presence of 'NaN' (CALCITE-4467). The respective ticket was closed and it
> was decided that it will be complicated to add special semantics to 'NaN'.
> However, to overcome the problem of "wrong" results DB engines such as Hive,
> Impala, etc., started applying workarounds for turning off simplifications
> under certain conditions.
> For example, Impala created a custom extension of
> [RexSimplify|https://github.com/apache/impala/blob/ac16a39210df9999f8dd1941e3fa513594f9aab2/java/calcite-planner/src/main/java/org/apache/impala/calcite/operators/ImpalaRexSimplify.java#L38]
> that inspects binary operators and does not simplify an expression if it
> contains approximate types.
> Although the RexSimplify class does not prevent overriding its not really
> made for extension and doing so creates problems in other places where a
> simplifier is needed.
> A better solution is to add built-in functionality in the standard
> RexSimplify class to be able to skip simplifications for certain expressions.
> The easiest and more general way to achieve that would be to allow callers to
> create a RexSimplify with a pluggable RexVisitor that decides if an
> expression must be simplified or not.
> Another more focused solution around 'Nan' would be to disallow
> simplifications on certain datatypes. For example, skip simplification on
> approximate numeric types.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
