SUM0 vs SUM

[Vladimir Sitnikov]

Hi,

As you might know, SUM aggregate returns null when aggregating the empty
set.
Optiq replaces SUM(x) with "case when COUNT(x)>0 then SUM0(x) else NULL
end" where SUM0 is guaranteed to have non-nullable type (returns 0 in case
of empty set).

I wonder why is that made and if we can drop that SUM0.

-- 
Regards,
Vladimir Sitnikov