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https://issues.apache.org/jira/browse/HIVE-287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879929#action_12879929
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John Sichi commented on HIVE-287:
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Sorry to chime in late on this one, but I have one big question on this one:
can we instead do it in a way which does not break the UDAF interface?
The existing patch adds a new method to the GenericUDAFResolver interface,
meaning all existing plugin implementations outside of the Hive codebase will
fail to compile (due to the fact that we did not already have the insulating
abstract base class available). We already have some of these within Facebook.
Let's analyze the two new parameters one by one.
isDistinct: this doesn't actually modify the choice of evaluator
implementation at all, since the actual duplicate elimination takes place
upstream of the UDAF invocation. So instead of adding this parameter, can we
instead add a new method supportsDistinct() on GenericUDAFEvaluator? Then call
this after instantiating the new evaluator in order to carry out the additional
validation.
isAllColumns: COUNT(*) is probably the only function which is ever even going
to care about this one. Couldn't we just use an empty array of TypeInfo to
indicate all columns?
Independent of the above, I think adding the insulating abstract base should
still be done now to make future transitions smoother when interface-breaking
is absolutely required. So keep that part of the patch.
> count distinct on multiple columns does not work
> ------------------------------------------------
>
> Key: HIVE-287
> URL: https://issues.apache.org/jira/browse/HIVE-287
> Project: Hadoop Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: Namit Jain
> Assignee: Arvind Prabhakar
> Attachments: HIVE-287-1.patch, HIVE-287-2.patch, HIVE-287-3.patch
>
>
> The following query does not work:
> select count(distinct col1, col2) from Tbl
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