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https://issues.apache.org/jira/browse/CALCITE-2556?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16613819#comment-16613819
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Julian Hyde edited comment on CALCITE-2556 at 9/13/18 5:29 PM:
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{quote}{{ReduceExpressionsRule}} uses {{RexSimplify}}.
That is basically the same code.{quote}
Not true. While it is true that {{ReduceExpressionsRule}} uses {{RexSimplify}},
it goes further. It is able to reduce 3 + 4 to 7, and {{RexSimplify}} is not
capable of that.
A few years ago I came up with a "cheap" expression reducer that did not use
Janino. We backed away from that, because of the danger was that it would make
mistakes on the corner cases. For example, does {{CAST(3.14159 AS DECIMAL(5,
4)) > CAST(3.14159 AS DECIMAL(4, 3))}} reduce to true or false? It depends on
the subtleties of the rules of type promotion. I don't even know the answer,
frankly.
Using RexFuzzer gives us a false sense of security. It uses RexInterpreter,
which is a "cheap" expression reducer.
I think we should draw the line at (3-valued) boolean expressions and
constraints. I don't think {{RexSimplify}} should be reducing expressions
involving integers or date-times, or expressions that use operators such as >,
MOD, SUBSTRING or CAST.
There might be a few exceptions to this rule if they are easy and
self-evidently correct.
was (Author: julianhyde):
{quote}{{ReduceExpressionsRule}} uses {{RexSimplify}}.
That is basically the same code.{quote}
Not true. While it is true that {{ReduceExpressionsRule}} uses {{RexSimplify}},
it goes further. It is able to reduce 3 + 4 to 7, and {{RexSimplify}} is not
capable of that.
> RexSimplify: not(trueLiteral) could be simplified to false
> ----------------------------------------------------------
>
> Key: CALCITE-2556
> URL: https://issues.apache.org/jira/browse/CALCITE-2556
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.17.0
> Reporter: Vladimir Sitnikov
> Assignee: Julian Hyde
> Priority: Major
>
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