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https://issues.apache.org/jira/browse/CALCITE-4073?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17159698#comment-17159698
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Danny Chen commented on CALCITE-4073:
-------------------------------------

Thanks. There was indeed a discussion on the mail list, hope we can make a 
consensus [1]

[1] 
https://lists.apache.org/x/thread.html/r24ce699508819b6f984b7de5078ff29e2ca293d1510fb32d0eab4fc1@%3Cdev.calcite.apache.org%3E

> Add a new component RexNormalize for more effect rex nodes normalization
> ------------------------------------------------------------------------
>
>                 Key: CALCITE-4073
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4073
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.24.0
>            Reporter: Danny Chen
>            Assignee: Danny Chen
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.24.0
>
>          Time Spent: 6h 10m
>  Remaining Estimate: 0h
>
> Currently, we only have simple normalization such as:
> $2 = $1 => $1 = $2
> $2 > $1 => $1 < $2
> we can extend the logic to more like:
> - put the complex predicates behind, like OR(OR(udf($1), $2), $3) => OR($3, 
> OR(udf($1), $2))
> - put the udf operand behind, like OR(udf($1), $2) => OR($2, udf($1))
> - put the local variables that appears more frequently in the front, which is 
> more user-friendly to code generation because the variable can be cached and 
> reused.
> Also note that, we should allows flexible configuration for switch this 
> function on/off(not a system calcite property now) for downstream users and 
> projects(because the normalization may have some performance trade-off).



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