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https://issues.apache.org/jira/browse/HIVE-655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12777390#action_12777390
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Ning Zhang commented on HIVE-655:
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Agree with Namit. A UDTF is a function returning a table, so it should appear
where any table/view could appear in the QL. Ideally it should only appear in
the FROM clause since that's the only place a table can appear, and the
semantics is well defined. If we really want to put UDTF in a SELECT clause for
backward compatibility reason, we'd better to limit the number of UDTF to 1 so
that it can only be used as a table in the subquery select * from (select UDTF
from ..). Otherwise we have to deal with the complexity of semantics for
queries such as select pageid, count(...), UDTF(...) from .. group by ... It is
new to users and it is hard to explain.
> Add support for user defined table generating functions
> -------------------------------------------------------
>
> Key: HIVE-655
> URL: https://issues.apache.org/jira/browse/HIVE-655
> Project: Hadoop Hive
> Issue Type: New Feature
> Components: Query Processor
> Reporter: Raghotham Murthy
> Assignee: Paul Yang
> Attachments: HIVE-655.1.patch, HIVE-655.2.patch
>
>
> Provide a way for users to add a table generating function, i.e., functions
> that generate multiple rows from a single input row. Currently, the only way
> to do it is via the TRANSFORM clause which requires streaming the data.
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