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https://issues.apache.org/jira/browse/PHOENIX-1987?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14582830#comment-14582830
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James Taylor commented on PHOENIX-1987:
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bq. Is math function order preserving means it is monotonic?
Yes
> 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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