Hi, in calcite, has the concept of sum0, here I quote the definition of sum0:
Sum0 is an aggregator which returns the sum of the values which go into it like Sum. It differs in that when no non null values are applied zero is returned instead of null.. One scenario is that we can use sum0 to implement pre-calculation count(pre-calculation system like Apache Kylin). It is very easy in Spark to implement sum0, if community consider this is necessary, I would like to open a JIRA and implement this. --- Regards! Aron Tao
