Jihong MA created SPARK-8800:
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Summary: Spark SQL Decimal Division operation loss of
precision/scale when type is defined as DecimalType.Unlimited
Key: SPARK-8800
URL: https://issues.apache.org/jira/browse/SPARK-8800
Project: Spark
Issue Type: Bug
Reporter: Jihong MA
According to specification defined in Java doc over BigDecimal :
http://docs.oracle.com/javase/1.5.0/docs/api/java/math/BigDecimal.html
When a MathContext object is supplied with a precision setting of 0 (for
example, MathContext.UNLIMITED), arithmetic operations are exact, as are the
arithmetic methods which take no MathContext object. (This is the only behavior
that was supported in releases prior to 5.) As a corollary of computing the
exact result, the rounding mode setting of a MathContext object with a
precision setting of 0 is not used and thus irrelevant. In the case of divide,
the exact quotient could have an infinitely long decimal expansion; for
example, 1 divided by 3. If the quotient has a nonterminating decimal expansion
and the operation is specified to return an exact result, an
ArithmeticException is thrown. Otherwise, the exact result of the division is
returned, as done for other operations.
when Decimal data is defined as DecimalType.Unlimited in Spark SQL, the exact
result of the division should be returned or truncated to precision = 38 which
is in align with what Hive supports. the current behavior is as shown
following, which cause we lose the accuracy of Decimal division operation.
scala> val aa = Decimal(2) / Decimal(3);
aa: org.apache.spark.sql.types.Decimal = 1
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