There is a problem with the stddev aggregation function.
When it calculates stddev aggregation for multiple records it works fine,
but when there is only one record in the group in returns null instead of zero.
Hello Asaf,
you are right, but this bug (http://bug.cloveretl.org/view.php?id=4323) has been already fix and the function returns proper value since the release that will be released this week (3.0.1).