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https://issues.apache.org/jira/browse/HIVE-474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12719368#action_12719368
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Min Zhou edited comment on HIVE-474 at 6/14/09 7:02 PM:
--------------------------------------------------------
I thought there is another special case here. If the query has multiple
distinct operations on the same column , we can push down the evaluation of
those expressions into reducers.
{code}
Query:
select a, count(distinct if(codition, b, null)) as col1, count(distinct
if(!condition, null, b)) as col2, count(distinct b) as col3
Plan:
Job :
Map side:
Emit: distribution_key: a, sort_key: a, b, value: nothing
Reduce side:
Group By
a, count col1, col2, col3 by evaluating their expressions
{code}
was (Author: coderplay):
I thought there is another special case here. If the query has multiple
distinct operations on the same column , we can push down the evaluation of
those expressions into reducers.
Query:
select a, count(distinct if(codition, b, null)) as col1, count(distinct
if(!condition, null, b)) as col2, count(distinct b) as col3
Plan:
Job :
Map side:
Emit: distribution_key: a, sort_key: a, b, value: nothing
Reduce side:
Group By
a, count col1, col2, col3 by evaluating their expressions
> Support for distinct selection on two or more columns
> -----------------------------------------------------
>
> Key: HIVE-474
> URL: https://issues.apache.org/jira/browse/HIVE-474
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Alexis Rondeau
>
> The ability to select distinct several, individual columns as by example:
> select count(distinct user), count(distinct session) from actions;
> Currently returns the following failure:
> FAILED: Error in semantic analysis: line 2:7 DISTINCT on Different Columns
> not Supported user
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