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https://issues.apache.org/jira/browse/CASSANDRA-18470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17714628#comment-17714628
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Nadav Har'El commented on CASSANDRA-18470:
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Benedict, I confirmed your worry in the last paragraph: The fact that the
implementation's is keeping only "avg" and not the sum and count separately
indeed makes this bug even worse:
Today, the AVG of _decimal_ values {*}1{*}, {*}2{*}, *2, 3* comes out as an 1,
while the correct result is 2.
So the current algorithm can be wrong even if we know a-priori that the result
is an integer.
> Average of "decimal" values rounds the average if all inputs are integers
> -------------------------------------------------------------------------
>
> Key: CASSANDRA-18470
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18470
> Project: Cassandra
> Issue Type: Bug
> Reporter: Nadav Har'El
> Priority: Normal
>
> When running the AVG aggregator on "decimal" values, each value is an
> arbitrary-precision number which may be an integer or fractional, but it is
> expected that the average would be, in general, fractional. But it turns out
> that if all the values are integer *without* a ".0", the aggregator sums them
> up as integers and the final division returns an integer too instead of the
> fractional response expected from a "decimal" value.
> For example:
> # AVG of {{decimal}} values 1.0 and 2.0 returns 1.5, as expected.
> # AVG of 1.0 and 2 or 1 and 2.0 also return 1.5.
> # But AVG of 1 and 2 returns... 1. This is wrong. The user asked for the
> average to be a "decimal", not a "varint", so there is no reason why it
> should be rounded up to be an integer.
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