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https://issues.apache.org/jira/browse/HIVE-4956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13828528#comment-13828528
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Amareshwari Sriramadasu commented on HIVE-4956:
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I agree with the concerns above that this is deviating from SQL. But it gives
lot of performance improvement in distributed systems. How about change the
separator to '+' instead of ',', as part of Hive QL?
The query will look like the following :
{noformat}
select t.x, t.y, .... from T1+T2 t where t.p1='x' OR t.p1='y' ...
[groupby-clause] [having-clause] [orderby-clause]
{noformat}
If the proposal is fine, I can upload the patch.
> 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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