Should skip NULL value in streaming min/max agg functions

[stdrc]

That is the behavior of batch mode and postgres.

[xxchan]

example:

create table t(x int);
insert into t values(NULL),(1);
create materialized view mv as select min(x) as min, max(x) as max from t;

dev=> select * from mv;
 min | max
-----+-----
     |   1
(1 row)

dev=> select min(x), max(x) from t;
 ?column? | ?column?
----------+----------
        1 |        1
(1 row)

[xiangjinwu]

related: #4272
Skipping null would fix the user-visible behavior. But it looks like the underlying logic is still seeing null as smaller than non-null values, while the expected behavior is that null being largest by default.