How to find current row number relative to window frame

Art Ruszkowski <a_@prudenttradingsystems.com> writes:

I have a user defined aggregate function and in Sfunc I need to
reference current row number relative to window frame. Ideallly I would like to have following construct:

select my_aggregate(x,current_row_number_relative_to window) over
(order by y rows between n preceding and current row) as..... from ….

Couldn't you make the aggregate track the current row number as part of
its state?

While it's a bit annoying to have to do that, I don't see any other
solution that doesn't involve converting the aggregate into a
full-fledged window function, which you probably don't want to do.
(Even then, nodeWindowAgg.c doesn't seem to expose a function for
row number within frame, only row number within partition.)

regards, tom lane

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