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From Aniket Mokashi <aniket...@gmail.com>
Subject Re: Does Hive 0.11 have Query Flattening optimizations?
Date Thu, 27 Jun 2013 21:30:04 GMT
Hi Mihir,

I am almost certain that both the queries will compile to the same MR plan
in hive (I haven't checked though).

In fact, having clause is a syntactic sugar to achieve whats done in the
nested query. Take a look at:
https://issues.apache.org/jira/browse/HIVE-1790

Thanks,
Aniket


On Wed, Jun 26, 2013 at 10:46 PM, Mihir Kulkarni <mihirk.31@gmail.com>wrote:

> Hello,
>
> Does hive support Query Flattening? For example a query like this:
>
> *SELECT alias.a0, alias.a1*
> *FROM*
> *            (SELECT COUNT(b) AS a0, c AS a1*
> *            FROM test*
> *            GROUP BY c) alias*
> *WHERE alias.a0 > 2;*
> *
> *
> would be flattened into:
>
> *SELECT COUNT(b), c*
> *FROM test*
> *GROUP BY c*
> *HAVING COUNT(b) > 2;*
>
> Does Hive (0.11) have such kind of optimizations or are they even useful
> considering all queries are ultimately converted into MapReduce jobs? At
> Informatica Corp we rely on Hive a lot and hence are interested to support
> such optimizations.
>
> Thanks in anticipation.
>
> Regards,
> *---*
> *Mihir Kulkarni
> **Software Engineer | Data Engine
> Informatica Corporation*
>



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