-single MR stage for join and group by
Chen Song 2013-08-01, 17:19
Suppose we have 2 simple tables
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?