Mark Hamstra created SPARK-13806:
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Summary: SQL round() produces incorrect results for negative values
Key: SPARK-13806
URL: https://issues.apache.org/jira/browse/SPARK-13806
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 1.6.1, 1.6.0, 2.0.0
Reporter: Mark Hamstra
Round in catalyst/expressions/mathExpressions.scala appears to be untested with
negative values, and it doesn't handle them correctly.
There are at least two issues here:
1) In the genCode for FloatType and DoubleType with _scale == 0, round() will
not produce the same results as for the BigDecimal.ROUND_HALF_UP strategy used
in all other cases. This is because Math.round is used for these _scale == 0
cases. For example, Math.round(-3.5) is -3, while BigDecimal.ROUND_HALF_UP at
scale 0 for -3.5 is -4.
Even after this bug is fixed with something like...
{code}
if (${ce.value} < 0) {
${ev.value} = -1 * Math.round(-1 * ${ce.value});
} else {
${ev.value} = Math.round(${ce.value});
}
{code}
...which will allow an additional test like this to succeed in
MathFunctionsSuite.scala:
{code}
checkEvaluation(Round(-3.5D, 0), -4.0D)
{code}
...there still appears to be a problem on at least the
checkEvalutionWithUnsafeProjection path, where failures like this are produced:
{code}
Incorrect evaluation in unsafe mode: round(-3.141592653589793, -6), actual:
[0,0], expected: [0,8000000000000000] (ExpressionEvalHelper.scala:145)
{code}
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