[ https://issues.apache.org/jira/browse/PHOENIX-1987?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14578129#comment-14578129 ] 

Shuxiong Ye commented on PHOENIX-1987:
--------------------------------------

Hi [~jamestaylor], 

Patch [1] adds tests in QueryCompilerTest to check optimization about ORDER BY.
Please help me to review it.

I have a question in my previous comment. Please give me some hints about it. : )

[1] 0001-PHOENIX-1987-fixing-getKeyFormationTraversalIndex-in-SIGN-function.patch

> SIGN built-in function should be order preserving
> -------------------------------------------------
>
>                 Key: PHOENIX-1987
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-1987
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Shuxiong Ye
>             Fix For: 5.0.0, 4.5.0, 4.4.1
>
>         Attachments: 0001-PHOENIX-1987-SIGN-built-in-function-should-be-order_v2.patch, 0001-PHOENIX-1987-fixing-getKeyFormationTraversalIndex-in-SIGN-function.patch
>
>
> The SIGN built-in function preserves the order of its input. This needs to be explicitly implemented in SignFunction by implementing the following method:
> {code}
>     public OrderPreserving preservesOrder() {
>         return OrderPreserving.YES;
>     }
> {code}
> This will allow certain optimizations reducing the amount of memory and/or buffering that is required if SIGN is used in a GROUP BY or ORDER BY clause.



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