mcvsubbu commented on issue #4230: NULL value support for all data types
URL: 
https://github.com/apache/incubator-pinot/issues/4230#issuecomment-497181413
 
 
   > @mcvsubbu is there an issue if the presence vector is always built?
   No issue, just that we change the behavior from what people are used to. I 
am guessing there is at least someone out there who relies on the fact that a 
null will be auto-populated by default null value. Many applications also set 
custom default null values in their schema.
   > 
   > If I understand things correctly, I believe the current state of handling 
nullables is a bit unfortunate. The scenario you mentioned is not just an issue 
for building presence vector, but, as @mayankshriv pointed out, it can actually 
result in incorrect aggregations.
   > 
   > Is the defaultNullValue of 0 just for metrics? Or is it based on datatype?
   0 for metrics, and Long.MIN or Int.MIN or "null" for dimensions.
   
   > In either case, should the actual behavior be corrected? We should not 
allow default "defaultNullValues" but we elevate the presence vector to a first 
class citizen - something that should always be present (no pun intended); if 
users provide a "defaultValue", we can use that if the column is missing for a 
row (and don't filter it out at any stage?)
   
   

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