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https://issues.apache.org/jira/browse/HIVE-3773?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13546230#comment-13546230
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Gang Tim Liu commented on HIVE-3773:
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thank you for great point.
Yes, it can. In addition, it can solve much complexer queries like join and
will bring other benefits.
This issue is targeted to solve the simple use case in a simple way. It will
benefit general purpose including the use case where configuration of 2206 is
not turned on.
> Share input scan by unions across multiple queries
> --------------------------------------------------
>
> Key: HIVE-3773
> URL: https://issues.apache.org/jira/browse/HIVE-3773
> Project: Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Namit Jain
> Assignee: Gang Tim Liu
>
> Consider a query like:
> select * from
> (
> select key, 1 as value, count(1) from src group by key
> union all
> select 1 as key, value, count(1) from src group by value
> union all
> select key, value, count(1) from src group by key, value
> ) s;
> src is scanned multiple times currently (one per sub-query).
> This should be treated like a multi-table insert by the optimizer.
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