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From "Wenchen Fan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-12770) Implement rules for branch elimination for CaseWhen in SimplifyConditionals
Date Tue, 12 Jan 2016 19:19:39 GMT

    [ https://issues.apache.org/jira/browse/SPARK-12770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15094569#comment-15094569
] 

Wenchen Fan commented on SPARK-12770:
-------------------------------------

a limitation for the first rule: we can only use that branch if it's true and is the FIRST
branch.

> Implement rules for branch elimination for CaseWhen in SimplifyConditionals
> ---------------------------------------------------------------------------
>
>                 Key: SPARK-12770
>                 URL: https://issues.apache.org/jira/browse/SPARK-12770
>             Project: Spark
>          Issue Type: Sub-task
>          Components: Optimizer, SQL
>            Reporter: Reynold Xin
>
> There are a few things we can do:
> 1. If a branch's condition is a true literal, remove the CaseWhen and use the value from
that branch.
> 2. If a branch's condition is a false or null literal, remove that branch.
> 3. If only the else branch is left, remove the CaseWhen and use the value from the else
branch.



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