| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
| Cc: | AgentM <agentm(at)themactionfaction(dot)com>, PostgreSQL General ML <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: SQL:2003 Window Functions for postgresql 8.3? |
| Date: | 2006-08-24 18:47:20 |
| Message-ID: | 8467.1156445240@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> The main thing I want to use them for is for cumulative output.
> ...
> With window functions you define for each row a "window" which is from
> the beginning of the table to that row and then sum the values, for
> each row. Then you just divide by the total, nice.
Egad. Wouldn't that involve O(N) memory and O(N^2) operations?
Perhaps an extremely smart optimizer could improve this using knowledge
of the specific aggregates' behaviors, but for "black box" aggregates
it sounds pretty unworkable.
regards, tom lane
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