Amareshwari Sriramadasu created HIVE-4956:
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Summary: Allow multiple tables in from clause if all them have the
same schema, but can be partitioned differently
Key: HIVE-4956
URL: https://issues.apache.org/jira/browse/HIVE-4956
Project: Hive
Issue Type: Improvement
Components: Query Processor
Reporter: Amareshwari Sriramadasu
Assignee: Amareshwari Sriramadasu
We have a usecase where the table storage partitioning changes over time.
For ex:
we can have a table T1 which is partitioned by p1. But overtime, we want to
partition the table on p1 and p2 as well. The new table can be T2. So, if we
have to query table on partition p1, it will be a union query across two table
T1 and T2. Especially with aggregations like avg, it becomes costly union query
because we cannot make use of mapside aggregations and other optimizations.
The proposal is to support queries of the following format :
select t.x, t.y, .... from T1,T2 t where t.p1='x' OR t.p1='y' ...
[groupby-clause] [having-clause] [orderby-clause] and so on.
Here we allow from clause as a comma separated list of tables with an alias and
alias will be used in the full query, and partition pruning will happen on the
actual tables to pick up the right paths. This will work because the difference
is only on picking up the input paths and whole operator tree does not change.
If this sounds a good usecase, I can put up the changes required to support the
same.
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