[jira] [Created] (ARROW-12911) sum of zero rows gives null; should give 0

["Adam Hooper (Jira)" <ji...@apache.org>]

Adam Hooper created ARROW-12911:
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             Summary: sum of zero rows gives null; should give 0
                 Key: ARROW-12911
                 URL: https://issues.apache.org/jira/browse/ARROW-12911
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++, Python
    Affects Versions: 4.0.1
            Reporter: Adam Hooper


{code}
>>> pa.compute.sum(pa.array([], pa.int64()))
<pyarrow.Int64Scalar: None>
{code}

I'd expect 0.

I can't think of any reason for NULL, except that SQL returns NULL. But I can't figure out why SQL returns NULL. Does anybody know? Any textbook -- and https://en.wikipedia.org/wiki/Summation -- specifies 0.

Pandas and Numpy return 0. Also, Apache Arrow c_glib implementation returns 0 -- and even tests for it: https://github.com/apache/arrow/blob/master/c_glib/test/test-int8-array.rb#L60



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