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Posted to dev@hive.apache.org by "Vineet Garg (JIRA)" <ji...@apache.org> on 2017/03/29 23:08:41 UTC

[jira] [Created] (HIVE-16330) Improve plans for scalar subquery with aggregates

Vineet Garg created HIVE-16330:
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             Summary: Improve plans for scalar subquery with aggregates
                 Key: HIVE-16330
                 URL: https://issues.apache.org/jira/browse/HIVE-16330
             Project: Hive
          Issue Type: Improvement
            Reporter: Vineet Garg
            Assignee: Vineet Garg


Scalar subquery plans are generated with a count(*) on subquery which is fed to {{sq_count_check}} UDF. This is to make sure at runtime that there is at most one row generated by scalar subquery. 

We can avoid generating this extra count(*) for scalar subqueries with aggregates and windowing since such queries are guaranteed to generate at most one row. e.g. {code:SQL} select * from part where p_size > (select max(p_size) from part) {code}



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