Re: Add RESPECT/IGNORE NULLS and FROM FIRST/LAST options

> The last time this was discussed (
> https://www.postgresql.org/message-id/1037735.1610402426%40sss.pgh.pa.us)
> it was suggested to make the feature generalizable, beyond what the
> standard says it should be limited to.

I have read the mail. In my understanding nobody said that standard
window functions should all accept the null treatment clause.

Also Tom said:
https://www.postgresql.org/message-id/5567.1537884439%40sss.pgh.pa.us
> The questions of how we interface to the individual window functions
> are really independent of how we handle the parsing problem. My
> first inclination is to just pass the flags down to the window functions
> (store them in WindowObject and provide some additional inquiry functions
> in windowapi.h) and let them deal with it.

As I said before I totally agree with this. With my patch if a
(custom) window function does not want to accept null treatment
clause, it just calls ErrorOutNullTreatment(). It will raise an error
if IGNORE NULLS or RESPECT NULLS is provided. If it does call the
function, it is up to the function how to deal with the null
treatment. In another word, the infrastructure does not have fixed
rules to allow/disallow null treatment clause for each window
function. It's "delegated" to each window function.

Anyway we can change the rule for other than nth_value etc. later
easily once my patch is brought in.

> With it generalizable, there would need to be extra checks for custom
> functions, such as if they allow multiple column arguments (which I'll add
> in v2 of the patch if the design's accepted).

I am not sure if allowing-multiple-column-arguments patch should be
provided with null-treatment patch.

> So I think we need a consensus on whether to stick to limiting it to
> several specific functions, or making it generalized yet agreeing the rules
> to limit it (such as no agg functions, and no functions with multiple
> column arguments).

Let's see the discussion...

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp