Re: [PATCH] Negative Transition Aggregate Functions (WIP)

Hi,

Reading over this, I realised that there is a problem with NaN
handling --- once the state becomes NaN, it can never recover. So the
results using the inverse transition function don't match HEAD in
cases like this:

create table t(a int, b numeric);
insert into t values(1,1),(2,2),(3,'NaN'),(4,3),(5,4);
select a, b,
       sum(b) over(order by a rows between 1 preceding and current row)
  from t;

which in HEAD produces:

 a |  b  | sum
---+-----+-----
 1 |   1 |   1
 2 |   2 |   3
 3 | NaN | NaN
 4 |   3 | NaN
 5 |   4 |   7
(5 rows)

but with this patch produces:

 a |  b  | sum
---+-----+-----
 1 |   1 |   1
 2 |   2 |   3
 3 | NaN | NaN
 4 |   3 | NaN
 5 |   4 | NaN
(5 rows)

Regards,
Dean