[jira] [Commented] (CALCITE-1413) New CASE statement simplification

["Zoltan Haindrich (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-1413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16646586#comment-16646586 ] 

Zoltan Haindrich commented on CALCITE-1413:
-------------------------------------------

opened [PR#886|https://github.com/apache/calcite/pull/886];

it actually contains ~4 somewhat distinct changes:

* a small refactor to make it more readable when the case branches are simplified/processed/etc - the fact that else's value didn't have condition made the processing kinda hard to read.
* simplification of case branches - this also makes a bug go away in case of {{RexUnknownAs.TRUE}} is used - I guess we right now don't actually use that...
* before boolean simplification
** case conditional are wrapped into {{IS TRUE}} blocks if needed
** return values are casted to the return type if needed
* addition of the new case conversion logic described in the jira description

[~julianhyde], [~jcamachorodriguez]: please let me know if you think this is too much at once - and I should be breaking this up into smaller parts

> New CASE statement simplification
> ---------------------------------
>
>                 Key: CALCITE-1413
>                 URL: https://issues.apache.org/jira/browse/CALCITE-1413
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.9.0
>            Reporter: Jesus Camacho Rodriguez
>            Assignee: Zoltan Haindrich
>            Priority: Major
>
> Another possible simplification for CASE statements that return boolean values.
> {code:sql}
> CASE
>  WHEN p1 THEN e1
>  WHEN p2 THEN e2
>  ELSE TRUE
> END
> {code}
> where e1...en are boolean expressions, can be rewritten into:
> {code:sql}
> (p1 and e1) or (p2 and e2 and not(p1)) or (not(p1) and not(p2))
> {code}
> if p1...pn cannot be nullable.



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