In calculating the STDDEV_SAMP/VARIANCE of N rows a divion by
N-1 rows is involved. Hence STDDEV_SAMP/VARIANCE for a single
row involves a division by 0. This change returns a NULL instead
of a 0 when calculating STDDEV_SAMP/VARIANCE for a single row.
STDDEV_POP/VARIANCE_POP for single row will still return a 0 since
this does not involve a division by 0. This matches the postgres
behavior.
Change-Id: Ide8af752cd8a2e554a2cd5a1ec948967a80de1fe
Reviewed-on: http://gerrit.cloudera.org:8080/5800
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: Impala Public Jenkins
c671ee1ece