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Date: Tue, 28 Jul 2009 23:48:15 -0700 (PDT)
From: "Min Zhou (JIRA)" <jira@apache.org>
To: hive-dev@hadoop.apache.org
Subject: [jira] Commented: (HIVE-607) Create statistical UDFs.
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    [ https://issues.apache.org/jira/browse/HIVE-607?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12736473#action_12736473 ] 

Min Zhou commented on HIVE-607:
-------------------------------

@Namit
I implemented group_cat() in a rush, and found something difficult slove: 
1. function group_cat() has a internal order by clause, currently, we can't such aggregation in hive. 
2. when the string will be group concated is too large, in another is appears data skew, there is ofen not  enough memory to store such a big string.

> Create statistical UDFs.
> ------------------------
>
>                 Key: HIVE-607
>                 URL: https://issues.apache.org/jira/browse/HIVE-607
>             Project: Hadoop Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: S. Alex Smith
>            Assignee: Emil Ibrishimov
>            Priority: Minor
>             Fix For: 0.4.0
>
>         Attachments: HIVE-607.1.patch, UDAFStddev.java
>
>
> Create UDFs replicating:
> STD() 	Return the population standard deviation
> STDDEV_POP()(v5.0.3) 	Return the population standard deviation
> STDDEV_SAMP()(v5.0.3) 	Return the sample standard deviation
> STDDEV() 	Return the population standard deviation
> SUM() 	Return the sum
> VAR_POP()(v5.0.3) 	Return the population standard variance
> VAR_SAMP()(v5.0.3) 	Return the sample variance
> VARIANCE()(v4.1) 	Return the population standard variance
> as found at http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html.

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