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https://issues.apache.org/jira/browse/KYLIN-3359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16473382#comment-16473382
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Zhong Yanghong commented on KYLIN-3359:
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To support sum case when ..., the columns for an expression can be classified
with two kinds. One is measure columns, and the other is dimension columns.
There are several preconditions that the expression can be pushed down to hbase:
* count() is predefined (which is always defined in kylin)
* {color:#f79232}sum(col) is predefined as a normal measure{color}
* {color:#f79232}The related filter for case when can be pushed down to
hbase{color}. Here, for simplification, the dimension columns for the filter
can only be from fact tables.
> Support sum(expression) if possible
> -----------------------------------
>
> Key: KYLIN-3359
> URL: https://issues.apache.org/jira/browse/KYLIN-3359
> Project: Kylin
> Issue Type: Sub-task
> Reporter: Zhong Yanghong
> Assignee: Zhong Yanghong
> Priority: Major
>
> The expression can be as follows:
> # a ~1~*col ~1~ + a ~2~*col ~2~ + ... + a ~n~*col ~n~ + b, if sum(col
> ~1~),sum(col ~2~),...sum(col ~n~) are defined
> # case when {{filter}} ~1~ then expr ~1~
> when {{filter}} ~2~ then expr ~2~
> ...
> else expr ~N~
> end, if {{filter}} ~1~,{{filter}} ~2~, ... {{filter}} ~N-1~, and expr
> ~1~,expr ~2~,...expr ~N~ are supported
> There's a constraint for the filter. That is it's able to push down the
> related filters in case when.
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