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Hive >> mail # user >> single MR stage for join and group by


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single MR stage for join and group by
Suppose we have 2 simple tables

A
id int
value string

B
id

When hive translates the following query

select max(A.value), A.id from A join B on A.id = A.id group by A.id;

It launches 2 stages, one for the join and one for the group by.

My understanding is that if the join key set is a sub set of the group by
key set, it can be achieved in the same map reduce job. If that is correct
in theory, could it be a feature in hive?

Chen
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Stephen Sprague 2013-08-02, 00:32
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Yin Huai 2013-08-02, 04:14
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Chen Song 2013-08-02, 17:32