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From "Xuefu Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-5848) Hive's type promotion isn't correct
Date Mon, 18 Nov 2013 23:45:21 GMT
Xuefu Zhang created HIVE-5848:
---------------------------------

             Summary: Hive's type promotion isn't correct
                 Key: HIVE-5848
                 URL: https://issues.apache.org/jira/browse/HIVE-5848
             Project: Hive
          Issue Type: Improvement
    Affects Versions: 0.12.0, 0.11.0, 0.10.0
            Reporter: Xuefu Zhang
            Assignee: Xuefu Zhang


When dealing with union all, arithmetic operators, and other places when type promotion is
needed or a common type is determined, Hive would promote non-exact data types (float and
double) to HiveDecimal. However, HIveDecimal is an exact type. Promoting a non-exact type
to an exact type makes a false impression to the user that the data is exact. For instance,
expression 3.14 + 3.14BD produces an HiveDecimal number 6.28. However, the two are not equivalent,
as the left operand is not exact. MySQL in this case produces a double 6.28, which is more
reasonable.

The problem was discovered in HIVE-3976. HIVE-5356 solves the problem for arithmetic operators,
but there are more places where the problem exists. For instance, HIVE-5825 manifested the
same issue.

The purpose of this JIRA is to revisit the type casting and type promotion to make HIVE's
behavior more in line with standard or other major database implementations.



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