On Sat, Jul 05, 2008 at 07:04:29PM +0900, H.Harada wrote:
> As I proposed a month before, I am working on window function.
> The problem is, as written in the "Things to discussed" section of the
> document, how you define window functions (e.g. RANK()). My idea is to
> treat them as specialized functions such as SET OF functions and mark
> it in pg_proc. But this doesn't resolve RANK() boundary problem.
Actually, I would make RANK() and ROW_NUMBER() act more like
aggregates. ISTM you have two kinds of window functions:
- aggregation: a result is calculated over a set and the result copied
across all the rows.
- order depenadant: same as above, but the result is different for each
I think you could make the latter work using the current aggregation
setup, just by calling the final_func for each row rather than just
once at the end.
That would make RANK() a normal aggrgate which returns the number of
distinct values seen so far (assuming input is ordered) and
ROW_NUMBER() is just an alias for COUNT().
I hope this is clear, let me know if it doesn't make sense.
Have a nice day,
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.
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