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From "Namit Jain (JIRA)" <j...@apache.org>
Subject [jira] Created: (HIVE-746) constant folding
Date Tue, 11 Aug 2009 02:11:14 GMT
constant folding
----------------

                 Key: HIVE-746
                 URL: https://issues.apache.org/jira/browse/HIVE-746
             Project: Hadoop Hive
          Issue Type: New Feature
          Components: Query Processor
            Reporter: Namit Jain


The constants are not folded at compile time:

for eg:

select 1+2 from src

will evaluate 1+2 for every row.

This becomes more interesting for scenarios like:

select unix_timestamp() from src;

The UDF should be evaluated only once, and the same value should be returned. However, currently,
we mark it as non-deterministic and evaluate it for every row.
This can have bad side-effects on partition pruning etc.

In MySQL, the same value is generated independent of the time taken for the query.

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