Tatsuo Ishii <ishii@postgresql.org> writes:
>> The latest version restricts it to lag, lead, first_value, last_value,
>> and nth_value. We can extend it in a subsequent patch if there's
>> demand?
> The restriction is required by the SQL standard. So I don't think we
> need to extend to other window functions.
The SQL spec does not believe that user-defined window functions are a
thing. So its opinion on this point is useless. I would think that
IGNORE NULLS is potentially useful for user-defined window functions,
and we should not be building anything that restricts the feature to
specific functions.
regards, tom lane