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From Gopal Vijayaraghavan <gop...@apache.org>
Subject Re: Top N query
Date Thu, 04 Jun 2015 21:55:58 GMT

> I does't understand about your solution. Could you please provide exact
>query?

...
 GROUP BY recommend_ratings2.movieid  ORDER BY Measure_0 DESC limit 2 ) T_0
ON ( recommend_ratings2.movieid <=> T_0.movieid_0)


Follow the docs on the mysql impl of the space-ship operator -
<https://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#operator
_equal-to>

The hive impl follows the same rules which is (a.x = b.x) OR (a.x is NULL
and b.x is NULL).

AFAIK, most of the complex optimizations are turned off in the presence of
null-safe operators.

Cheers,
Gopal








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