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https://issues.apache.org/jira/browse/KYLIN-3361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17115707#comment-17115707
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ASF subversion and git services commented on KYLIN-3361:
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Commit 873d42c59943209f0aad6d06f041e95265c44bad in kylin's branch
refs/heads/master from Zhong, Yanghong
[ https://gitbox.apache.org/repos/asf?p=kylin.git;h=873d42c ]
KYLIN-3361 Add a two layer udaf stddev_sum
> Support stddev as a new measure
> -------------------------------
>
> Key: KYLIN-3361
> URL: https://issues.apache.org/jira/browse/KYLIN-3361
> Project: Kylin
> Issue Type: New Feature
> Reporter: Zhong Yanghong
> Assignee: Zhong Yanghong
> Priority: Major
> Fix For: v3.1.0
>
>
> (x ~1~ - +x+) ^2^ + (x ~2~ - +x+) ^2^ + ... + (x ~n~ - +x+) ^2^ = x ~1~ ^2^ +
> x ~2~ ^2^ + ... + x ~n~ ^2^ - n +x+ ^2^, where +x+ is the average of x ~1~, x
> ~2~, ..., x ~n~. Therefore, to compute stddev, what kylin need to do is to
> pre-calculate sum(x ~i~ ^2^), sum(x ~i~) and count
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